The very famous www.getdeb.net website for providing a LOT of packages for Ubuntu including Games, Audio, Multimedia, Development...etc has created a project (still in beta stage till the time of this entry) which aims at providing a repository specialized in Games ONLY! This is so as to enable the website users to get the latest games and their updates without having to download them manually.
I think it's a nice-to-have idea! Anyway, It was called Playbuntu at first, but due to some problems with Canonical (The company behind Ubuntu), it's now called Playdeb.
To install the new repo in Ubuntu, you just need to download and install two extra packages:
apturl-package and the playdeb package. The first one is for solving a bug that existed in Ubuntu Hardy (8.04), but I found out that I have a newer version on my Ubuntu (Intrepid Ibex), so I just installed the second one. Have fun :-)
The website URL: http://www.playdeb.net/