Some additions:
* MuCommander (Norton Commander-style file manager) * ShiftIt (window management/"Aero Snap"/Moom alternative) * Isolator (widow focus indicator) * SecondBar (menu bar for your second monitor) * KeyRemap4Macbook/PCKeyboard Hack (remap keys, capslock=command, etc.) * BetterTouchTool (trackpad gestures, middle click!)
Some additions: