There are plenty of window management apps on the Mac platform. Some allow you to snap windows to the edges of your screen like BetterSnapTool, but others, like Autumn Apps' Breeze (which we covered last year), allow you to record a desired window size and position.
Breeze sits in your menu bar and lets you define "states" of windows by positioning them on your screen wherever you want and selecting "Save State As." You can save states for one application and apply them to any window from any program or just for that one specific program. States can be bound to keyboard shortcuts or selected from a drop-down list from the menu bar.
Once you've got all the window states you want defined, you can quickly and easily move your windows around with just a few key presses.
Some programs don't react well to being manhandled like that, with one poignant example being Photoshop, but most programs behave as they should. If for some reason you have a problem with a window (maybe it moves too far off screen), Breeze has a handy "Rescue window" function that brings the window back on-screen for you to deal with.
There's a free trial available from Autumn Apps' website, while purchasing the app will set you back US$8. Breeze works on Mac OS X 10.5 and up, including PPC-based Macs.