Coda
Transmit
iWork 08
OmniGraffle
Mind Node
Pixelmator
Snapz X
Camino
Firefox
Opera
Yahoo! Messenger
Nicecast
PathFinder
1Password
Audial Hub
Visual Hub
CoverSutra
Onyx
Acquistion
Transmission
SuperDuper
-- yeah, I'm a big supporter of smaller software houses!
All these and some other software bought directly from the developers, or in bundles like MacHeist. But you know what? In fact, I never bought software as a Windows user. There's a great thing about Mac software: there are valuable options coming from smaller software houses.
And they're so cheap! I spent way less buying all of these than a copy of MS Office (here in Brazil it costs like 700 USD).