1 - Smashing Magazine. This is usually my first stop, and often I don't need to look any further. Here is their latest collection:
Free WordPress Themes: 2011 Edition - Smashing Magazine
2 - Blogex. This is another great resource for WordPress theme information:
Best WordPress Themes of 2011 (UPDATED)
I've seen a few "what is the best free theme" posts lately, so I thought this might help. Or maybe you've been bitten by the "theme bug" as well - if you have then these pages probably have the cure!