Drupal 7 (D7) hasn't been released yet, but there already are some themes compatible with D7. Here are some of them :
- Forest Floor - OK - kind of gray
- Dingus - Mostly CSS - no custom PHP
- mulpo - Clean and interesting
- Moleskine - Nice and rustic - derived from Basic theme
- NineSixty - Kind of plain
- AD Blueprint - Looks OK - clean
- AD The Morning After - Clean, spartan look
- Abessive - Unique, but a little too stark
- Basic - Based on Zen theme. Allows you to use Skinr module and SASS CSS.
- Smashing Dilectio - Interesting - quite colorful - ABANDONED
- Chameleon - Pure PHP-based theme - formerly in core
- Omega - 960gs-based theme. Seems to have lots of options.
- .mobi - For mobile version of your site
- Nifty 50 - Simple and clean
- Cherry Blossom - Has potential, but too pink for me
- camsel - A little too 'contemporary' for me
- Abaca - dark background with white text
- PocketT - For simple blogs
- Bluemarine ETS - - Easy Template System theme engine.
- Diary - For blogs - has cool calendar marks for entries
- web110 - A little too imposing for me
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Basic - OK
Seven - OK, but one col
Garland - not bad - smooth colors
Analytic - OK
Zen - OK
Genesis sub - OK
Genesis - OK
960 gs - NO - broken
Forest floor - Broken
Mulpo - broken
Stark - Clunky