I use Adium. I like Adium. I need Adium. Then, from left to right: CalendarBar (shows iCal and Facebook events as well as birthdays), Dropbox (icon seems not to be disableable), Espionage (password encryption for single folders), Jumpcut (Clipboard history with perfect system integration), Little Snitch Monitor (firewall), LittleSnapper (screenshots), WiFi, Time Machine (currently running…), Battery, Keyboard (ugliest icon ever produced by Apple), Clock, Hotspot Shield (Germans also want to use Hulu…), and Spotlight.
(From Nathanael)