I would recommend Better Touch Tool over SizeUp. It allows you to setup keyboard shortcuts as well as touchpad gestures to resize windows, and do a lot of other actions.
Yes! I love that software. I used it to make the gestures the same between my touchpad and my magic mouse. It's stupid how it's 3 fingers on one and 2 on the other.
I was also surprised not seeing Better Touch Tool there. It is a great program.
For example, I've mapped switching between tabs to TipTap left and TipTap right for any software that has tabs (Chrome, FireFox, Terminal, TextMate, etc.).