ClickyThere is now a dedicated repository for Ubuntu users who want to get new GPU drivers quickly - say you've bought a new GPU and it isn't supported by the default drivers.
The basic gist of it is:
Add these lines to your sources list:
(replace the word jaunty with the version you are using - hardy, intrepid, jaunty, karmic and onwards
then save this
http://keyserver.ubuntu.com:11371/pks/lookup?op=get&search=0x4F191A5A8844C542 to your desktop and import it under the "authentication" tab.
I haven't tried it myself yet, so take no responsibility for any unforeseen weirdness.