MondoMouse is a great OS X add-on to make life with the Rodent much easier. Given that we are talking about OS X, this is also quite needed, as I have to reach for the mouse far more often than I was used to, back when I was using Ion.
I have been using MondoMouse for about a year now, and I am quite happy with it. It has many features, but I am mainly using it to resize windows, and move them around: instead of navigating to the window frame, I just hold down the configured modifier keys, and move the mouse. The window below the mouse pointer moves along with the pointer. No click-to-front or careful positioning needed!
The latest release, version 1.4, supports resizing windows from any corner, a feature which I have long wished for!