I set my profile to the the 14w30b snapshot and ran the launcher. Once everything was downloaded the game launched and I created a creative mode world, with all default settings (New World name, etc.). The world was created and after a few seconds of my snow forest surroundings rendering in, the game crashed. The incrementing block was:

– Block model being tesselated –
Details:
Block: minecraft:grass[snowy=false]
Block location: World: (-244,85,204), Chunk: (at 12,5,12 in -16,12; contains blocks -256,0,192 to -241,255,207), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Using AO: true

I then started the game again and created a new world, and after spawning in a plain exactly the same thing happened. This time however:

– Block model being tesselated –
Details:
Block: minecraft:leaves[check_decay=false,decayable=true,variant=oak]
Block location: World: (-111,68,259), Chunk: (at 1,4,3 in -7,16; contains blocks -112,0,256 to -97,255,271), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Using AO: true

I don't have custom models, I just use a 64x texture pack with the vanilla models etc.