This is an amazing bit of freeware. Frequently updated, nice interface, tons of keyboard shortcuts, and good documentation. I shopped around for list manager/GTD programs and I haven't found anything better than this. The menubar icon is excellent, and there are several other options for quickly adding tasks or pieces of information (quicksilver integration, keyboard shortcuts for safari, mail, finder).

I haven't used the growl support, but that seems like a nice touch too.

Recommended all the way.