Tera Wurfl for Drupal
WURFL underwent licensing changes a little while back, and I stopped using it.

I either use Mobile Tools if I need all of the features it provides (mainly Panels integration) or I use get_browser directly (make sure you have a recent browscap.ini).  

I don't think Mobile Tools has a stable Drupal 7 release, though.

There is also the Drupal Browscap module, which purports to be better than the native version, though, I just manually keep my browscap.ini up-to-date.