Task management: Toodledo, http://www.toodledo.com. Different than Remember The Milk, maybe better. I’m trying it out and may switch permanently.
BetterTouchTool: http://www.boastr.de/. Lots of gestures for your Mac.
BetterSnapTool: http://blog.boastr.net/?page_id=2342. A subset of the gestures in BetterTouchTool, but in addition allows you to move a window by pressing a modifier key and moving the mouse. If you use a touchpad, this is actually just a modifier key and dragging your finger.
All are free.