Where can I find tall grass?

I've been going through a newly-generated world, traveling across several biomes, and I've seen tall grass everywhere there's regular grass: forests, savannah, plains, etc.

The only biomes in which it doesn't seem to spawn are tundra, deserts, and (of course) the Nether.

Tall grass is incredibly common: If you haven't seen a ton of it already, one thing to keep in mind is that new terrain features generally don't spawn on already-generated chunks, and you'll have to travel to a new, unexplored area to see them.

To confirm this, I loaded an existing world I had which spanned a few different biomes (tundra, taiga, forest, grassland). There was no tall grass in any of the pre-generated chunks. However, I found several instances of tall grass immediately after walking into an area that caused the game to generate a new chunk.

Edit (thanks, Kurley): as of 1.6.6, you can spawn tall grass yourself:

When applied to a grass block, one bone meal is consumed and tall grass, and occasionally flowers, forms around and on the grass block.

If you don't want to travel, you can use bone meal on grass to make either tall grass or flowers.