Best File System for Sharing Between OS X and Windows
If you're working exclusively with Win7 machines (i.e. no Vista or XP), and 10.6.6 or greater on the Mac side, try exFAT. Native read/write support under Win7 and OS X, and none of the file size limits of FAT32. Disk Utility will happily format your drives using it.

As long as you don't need legacy support, it's probably your best option, as it avoids any user-space filesystem drivers, which personally make me a bit uneasy.

Addendum: XP and Vista do support exFAT, Vista as of SP1, and XP with SP2 and the KB955704 update