From Infinite Labs:
Afloat is a Cocoa extender that adds both useful window management and nice eye candy to most Mac applications. It can keep windows on top, make them transparent or unclickable, move them or resize them without having to reach for the title bar or corner, and more.
What's new in this version:
This new version of the Afloat package is compatible with Snow Leopard.
Per a review on CNET, I added this. I rarely add applications especially with my new Macbook Pro. But I do use 'spaces' and have multiple screens open for work, play, music, etc. And it is an inconvenience switching when chatting using Yahoo or Skype. I thought that would solve the problem. However...afloat states it is unable to support either of these. Now I did not try anything else as I only needed it for these two. Yet...it did not work for me.