I've separated them into Mac / Windows
Browser: Firefox with Taboo, Split pane, TabMix, and TreeView / Chrome
Music Player: iTunes, Play (sbooth) or VLC for FLAC / WMP
OS: Leopard / XP, soon to be 7
Word Processor: NeoOffice, OpenOffice / OpenOffice
Image Editor: Seafoam, The GIMP / mspaint, Paint.net
3d Editor: nothing, sometimes Blender / trueSpace3.2
Audio Editing: Logic Studio, Audacity, ProTools LE 7.4, FMOD, pureData (saving up for MaxMSP) / FL Studio demo for fun
Video Editing: Quicktime Pro 7, iMovie 06 / Windows Movie Maker
IM'ing: iChat / don't do much im'ing, but I downloaded Live Messenger
Anti-Virus: ClamAV / Avira, SuperantiSpyware
Music Notation: Sibelius 6
IDE/Programming: Netbeans, TextWrangler / VC++ Express 2008, DBPro, CodeSurge
Game Engines: JMonkeyEngine / DBPro, DarkGDK, HL2, UT3
Games: Nothing, I refuse to settle for ports / L4D, TF2, Fallout 3, Civ4
Have I mentioned how much I love Netbeans?