If this helps at all...
Time: 04/10/14 10:56
Description: Applying mipmap

java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Unknown Source)
at sun.misc.IOUtils.readFully(Unknown Source)
at java.util.jar.JarFile.getBytes(Unknown Source)
at java.util.jar.JarFile.getManifestFromReference(Unknown Source)
at java.util.jar.JarFile.getInputStream(Unknown Source)
at sun.misc.URLClassPath$JarLoader$2.getInputStream(Unknown Source)
at sun.misc.Resource.cachedInputStream(Unknown Source)
at sun.misc.Resource.getByteBuffer(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at cue.d(SourceFile:286)
at cua.b(SourceFile:159)
at cua.a(SourceFile:77)
at cxh.j(SourceFile:553)
at cxh.a(SourceFile:139)
at cxk.a(SourceFile:23)
at cvt.a(SourceFile:99)
at bsu.aj(SourceFile:437)
at bsu.a(SourceFile:299)
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.util.Arrays.copyOf(Unknown Source)
at sun.misc.IOUtils.readFully(Unknown Source)
at java.util.jar.JarFile.getBytes(Unknown Source)
at java.util.jar.JarFile.getManifestFromReference(Unknown Source)
at java.util.jar.JarFile.getInputStream(Unknown Source)
at sun.misc.URLClassPath$JarLoader$2.getInputStream(Unknown Source)
at sun.misc.Resource.cachedInputStream(Unknown Source)
at sun.misc.Resource.getByteBuffer(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at cue.d(SourceFile:286)

– Sprite being mipmapped –
Details:
Sprite name: minecraft:blocks/redstone_block
Sprite size: 512 x 512
Sprite frames: 32 frames
Mipmap levels: 4
Stacktrace:
at cua.b(SourceFile:159)
at cua.a(SourceFile:77)
at cxh.j(SourceFile:553)
at cxh.a(SourceFile:139)
at cxk.a(SourceFile:23)
at cvt.a(SourceFile:99)
at bsu.aj(SourceFile:437)

– Initialization –
Details:
Stacktrace:
at bsu.a(SourceFile:299)
at net.minecraft.client.main.Main.main(SourceFile:120)

– System Details –
Details:
Minecraft Version: 1.8
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 524848 bytes (0 MB) / 1060372480 bytes (1011 MB) up to 1060372480 bytes (1011 MB)
JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 1.8
LWJGL: 2.9.1
OpenGL: AMD Radeon HD 7800 Series GL version 4.4.12874 Compatibility Profile Context 14.100.0.0, ATI Technologies Inc.
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: [sphax]
Current Language: English (UK)
Profiler Position: N/A (disabled)

What I expected to happen was...:
The game to open

What actually happened was...:
A crash screen

Steps to Reproduce:
1. Set game to Lastest Version
2. Press play
3. Crash