When in creative, go to the decoration blocks tab. Scroll down to the point where (I believe) the banners should be. This causes the game to crash. I haven't seen other people having this problem though, so I'm not really sure whether this is a bug or something to do with my computer.
(Can also be done by typing in 'ba' in the search tab)

---- Minecraft Crash Report ----
// On the bright side, I bought you a teddy bear!

Time: 27-7-14 12:01
Description: Registering texture

java.lang.IllegalArgumentException: Unknown image type 0
at java.awt.image.BufferedImage.<init>(Unknown Source)
at csa.a(SourceFile:40)
at csn.a(SourceFile:56)
at clu.a(SourceFile:122)
at clu.a(SourceFile:70)
at clu.a(SourceFile:22)
at cly.a(SourceFile:114)
at cly.a(SourceFile:107)
at chp.a(SourceFile:32)
at cop.a(SourceFile:98)
at cop.a(SourceFile:334)
at cop.b(SourceFile:368)
at bxd.a(SourceFile:249)
at bxd.a(SourceFile:107)
at bxv.a(SourceFile:36)
at bxr.a(SourceFile:548)
at cht.b(SourceFile:1007)
at brp.ar(SourceFile:896)
at brp.a(SourceFile:311)
at net.minecraft.client.main.Main.main(SourceFile:120)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at java.awt.image.BufferedImage.<init>(Unknown Source)
at csa.a(SourceFile:40)

– Resource location being registered –
Details:
Resource location: minecraft:b15
Texture object class: csa
Stacktrace:
at csn.a(SourceFile:56)
at clu.a(SourceFile:122)
at clu.a(SourceFile:70)
at clu.a(SourceFile:22)

– Block Entity Details –
Details:
Name: Banner // bbf
Stacktrace:
at cly.a(SourceFile:114)
at cly.a(SourceFile:107)
at chp.a(SourceFile:32)
at cop.a(SourceFile:98)
at cop.a(SourceFile:334)

– Item being rendered –
Details:
Item Type: ajb@1533badd
Item Aux: 15
Item NBT: null
Item Foil: false
Stacktrace:
at cop.b(SourceFile:368)
at bxd.a(SourceFile:249)
at bxd.a(SourceFile:107)
at bxv.a(SourceFile:36)
at bxr.a(SourceFile:548)

– Screen render details –
Details:
Screen name: bxr
Mouse location: Scaled: (420, 204). Absolute: (841, 296)
Screen size: Scaled: (683, 353). Absolute: (1366, 706). Scale factor of 2

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [cha['GrmpfhcGames'/189, l='MpServer', x=-204,55, y=70,00, z=31,64]]
Chunk stats: MultiplayerChunkCache: 289, 289
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: -204,00,64,00,36,00 - World: (-204,64,36), Chunk: (at 4,4,4 in -13,2; contains blocks -208,0,32 to -193,255,47), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 2039 game time, 2039 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 85 total; [cha['GrmpfhcGames'/189, l='MpServer', x=-204,55, y=70,00, z=31,64], abk['Bat'/22006, l='MpServer', x=-249,00, y=16,83, z=81,70], abk['Bat'/17, l='MpServer', x=-253,56, y=16,77, z=86,36], afg['Skeleton'/16, l='MpServer', x=-260,53, y=24,00, z=29,13], abk['Bat'/19, l='MpServer', x=-239,32, y=14,01, z=53,66], afg['Skeleton'/18, l='MpServer', x=-254,50, y=16,34, z=29,69], aci['Squid'/21, l='MpServer', x=-256,78, y=56,28, z=83,41], abk['Bat'/20, l='MpServer', x=-253,25, y=22,10, z=72,25], aci['Squid'/23, l='MpServer', x=-252,78, y=50,91, z=88,75], abk['Bat'/7879, l='MpServer', x=-247,44, y=17,21, z=78,10], adh['item.item.dyePowder.black'/22, l='MpServer', x=-249,44, y=38,00, z=82,34], aft['Zombie'/25, l='MpServer', x=-219,94, y=15,00, z=-8,53], aec['Enderman'/2607, l='MpServer', x=-185,50, y=13,00, z=7,50], afg['Skeleton'/27, l='MpServer', x=-244,09, y=26,00, z=3,38], abk['Bat'/26, l='MpServer', x=-239,75, y=29,10, z=-2,28], aft['Zombie'/29, l='MpServer', x=-233,50, y=24,00, z=7,03], aft['Zombie'/2603, l='MpServer', x=-196,13, y=12,00, z=1,78], afg['Skeleton'/28, l='MpServer', x=-237,94, y=28,00, z=7,44], aft['Zombie'/30, l='MpServer', x=-234,50, y=24,00, z=1,50], aft['Zombie'/4782, l='MpServer', x=-159,72, y=11,31, z=54,72], abk['Bat'/28428, l='MpServer', x=-225,48, y=27,09, z=17,70], aft['Zombie'/38, l='MpServer', x=-222,50, y=15,00, z=-4,50], aea['Creeper'/39, l='MpServer', x=-220,41, y=14,00, z=-4,94], aft['Zombie'/4779, l='MpServer', x=-160,44, y=13,00, z=52,94], abk['Bat'/28430, l='MpServer', x=-221,26, y=23,90, z=15,97], aft['Zombie'/42, l='MpServer', x=-211,50, y=14,00, z=-6,50], aea['Creeper'/43, l='MpServer', x=-209,50, y=12,00, z=-15,06], afs['Witch'/40, l='MpServer', x=-213,50, y=15,00, z=-5,50], afs['Witch'/41, l='MpServer', x=-221,44, y=13,00, z=-15,13], aft['Zombie'/46, l='MpServer', x=-215,50, y=21,00, z=-13,50], aea['Creeper'/47, l='MpServer', x=-221,50, y=22,00, z=-3,50], abk['Bat'/6005, l='MpServer', x=-179,68, y=11,05, z=-0,17], afg['Skeleton'/44, l='MpServer', x=-218,50, y=21,00, z=-12,50], afg['Skeleton'/45, l='MpServer', x=-218,81, y=23,00, z=3,16], afg['Skeleton'/51, l='MpServer', x=-220,50, y=30,00, z=47,50], afo['Spider'/50, l='MpServer', x=-210,50, y=13,00, z=6,50], aci['Squid'/49, l='MpServer', x=-212,31, y=48,38, z=-11,31], aci['Squid'/48, l='MpServer', x=-223,66, y=50,56, z=-11,53], aft['Zombie'/55, l='MpServer', x=-211,88, y=22,00, z=80,53], aft['Zombie'/54, l='MpServer', x=-218,03, y=24,00, z=89,41], aft['Zombie'/53, l='MpServer', x=-208,50, y=24,00, z=56,50], afg['Skeleton'/52, l='MpServer', x=-212,50, y=24,00, z=51,50], abk['Bat'/28433, l='MpServer', x=-218,20, y=25,19, z=14,57], aci['Squid'/59, l='MpServer', x=-218,88, y=60,81, z=83,59], aci['Squid'/58, l='MpServer', x=-218,81, y=59,03, z=86,00], adh['item.item.dyePowder.black'/57, l='MpServer', x=-215,47, y=47,00, z=80,50], abk['Bat'/28434, l='MpServer', x=-226,67, y=27,80, z=10,58], aft['Zombie'/56, l='MpServer', x=-217,38, y=23,00, z=91,81], abk['Bat'/12499, l='MpServer', x=-262,96, y=14,99, z=-40,84], aft['Zombie'/68, l='MpServer', x=-204,50, y=28,00, z=84,50], afg['Skeleton'/69, l='MpServer', x=-194,88, y=27,00, z=92,53], abk['Bat'/70, l='MpServer', x=-196,25, y=29,10, z=90,41], afg['Skeleton'/71, l='MpServer', x=-194,34, y=26,00, z=94,31], afg['Skeleton'/64, l='MpServer', x=-194,91, y=19,00, z=-34,41], aft['Zombie'/65, l='MpServer', x=-195,50, y=11,00, z=8,50], aci['Squid'/66, l='MpServer', x=-188,13, y=55,71, z=31,46], aea['Creeper'/67, l='MpServer', x=-194,31, y=25,00, z=95,47], aci['Squid'/73, l='MpServer', x=-208,88, y=59,28, z=90,66], aci['Squid'/85, l='MpServer', x=-182,31, y=59,91, z=91,41], aci['Squid'/84, l='MpServer', x=-187,88, y=62,53, z=90,50], aci['Squid'/86, l='MpServer', x=-190,00, y=59,22, z=95,38], aci['Squid'/81, l='MpServer', x=-190,28, y=48,56, z=7,94], aft['Zombie'/83, l='MpServer', x=-186,50, y=12,00, z=67,50], aci['Squid'/82, l='MpServer', x=-192,53, y=53,44, z=2,88], afs['Witch'/103, l='MpServer', x=-156,50, y=17,00, z=-34,50], afo['Spider'/98, l='MpServer', x=-173,50, y=19,00, z=105,50], aea['Creeper'/97, l='MpServer', x=-164,31, y=14,00, z=104,50], aci['Squid'/110, l='MpServer', x=-148,59, y=48,00, z=44,97], aft['Zombie'/111, l='MpServer', x=-144,59, y=15,00, z=53,09], afg['Skeleton'/108, l='MpServer', x=-143,53, y=14,00, z=57,84], abk['Bat'/109, l='MpServer', x=-152,83, y=17,91, z=31,48], aft['Zombie'/106, l='MpServer', x=-148,31, y=14,00, z=-29,34], aft['Zombie'/107, l='MpServer', x=-159,50, y=15,00, z=42,50], aea['Creeper'/104, l='MpServer', x=-149,44, y=15,00, z=-30,59], aea['Creeper'/105, l='MpServer', x=-145,50, y=15,00, z=-31,50], afo['Spider'/119, l='MpServer', x=-143,47, y=23,00, z=-31,31], afg['Skeleton'/113, l='MpServer', x=-144,50, y=13,00, z=98,50], aea['Creeper'/112, l='MpServer', x=-147,03, y=14,00, z=52,53], aft['Zombie'/127, l='MpServer', x=-139,50, y=34,00, z=110,50], afg['Skeleton'/126, l='MpServer', x=-142,50, y=13,00, z=99,50], afg['Skeleton'/125, l='MpServer', x=-139,66, y=12,00, z=100,69], afg['Skeleton'/124, l='MpServer', x=-140,50, y=13,00, z=99,50], afg['Skeleton'/123, l='MpServer', x=-129,50, y=20,00, z=48,50], aea['Creeper'/122, l='MpServer', x=-140,41, y=16,00, z=48,00], aft['Zombie'/121, l='MpServer', x=-139,50, y=16,00, z=46,50]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at ccz.a(SourceFile:308)
at brp.b(SourceFile:2254)
at brp.a(SourceFile:320)
at net.minecraft.client.main.Main.main(SourceFile:120)

– System Details –
Details:
Minecraft Version: 14w30c
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.6.0_15, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
Memory: 80854800 bytes (77 MB) / 428605440 bytes (408 MB) up to 954466304 bytes (910 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
Launched Version: 14w30c
LWJGL: 2.9.1
OpenGL: GeForce G 103M/PCI/SSE2 GL version 3.3.0, NVIDIA Corporation
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: No
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs: []
Current Language: English (US)
Profiler Position: N/A (disabled)