A few days ago, I ordered some PLA (from UltiMachine, at $47.50) so I could print out larger objects without warping. It's arrived, and now I have to figure out how to modify my MakerBot to use it. I found this thread helpful.
Just so you know, MakerBot Industries is also selling PLA, but it is 4032D, and is currently on sale at $60 (and will rise to $80 on Monday). Supposedly, 4032D is better because it has a more ABS-like melting point so it can be used in a MakerBot more easily, but I've heard 4042D works fine.