TwoUp
Have you seen the new Snap feature on Windows 7? I have, and was more than a little jealous when I found out about it; I constantly need two app windows to share the same screen and find it so annoying trying to resize them to fit. I found this awesome little gem that does just that. It’s called TwoUp made by Irradiated Software and turns this annoying chore into inconsequence. The best reason to use it, apart from the obvious, is that it’s free, so click here to visit the developer’s site and download that sucker!
TwoUp also has a bigger brother, SizeUp that allows you to not only split your windows 50/50, but in quarters and more besides.
PS. This is just a personal recommendation, I have not been asked to write this.
Enjoy