I have been keeping an index of companies from the current batch as they launch, with short descriptions and web traffic stats. Right now 27 of the 47 companies have already publicly launched (mostly on TechCrunch). I will update this throughout the day: http://www.daniellemorrill.com/2013/03/preliminary-yc-index-...

I'm not sure how complete it is, but HN user citizenkeys keeps a nice index of YC companies listed by batch.

http://ycuniverse.com/ycombinator-companies#ycw13

Check out my site: Seed-DB (http://www.seed-db.com). In addition to Y Combinator, I have data on 150+ accelerators around the world.

(YCList gets data from Seed-DB, for example)

Here is one that seems to be pretty accurate

http://yclist.com/