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.
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.).
To add more gestures for my touchpad (like TipTap-Left to switch tabs in every application that has them) I use Better Touch Tool.