[arizonagroove]

Windows Media Components for QuickTime
MacFUSE + sshfs
iTuneMyWalkman
AppleJack
MacPorts
Text Wrangler
Desktop Manager
Firefox (Safari's OK, but Firefox is better.)
Red Pill
Bombich Software (If you manage/deploy Macs)
StartupSound.prefPane
Keyboard Map for a UK PC style keyboard

I wouldn't say any of them are essential. What you may consider essential someone else may consider a waste of disk space.