Here's something I've been looking for for a long time! It's not an addon itself, but it does make the management and upkeep of your addons a lot simpler.
Cairnehoof of Dethecus (US) sent this in to Mike, who kindly sent it my way:
I read your article on wowinsider (big fan btw) about the addon issue in the upcoming patch. I have come across an great application for windows that updates your addons from all the popular sites. Maybe you could share it on the site. I know many people would love it. It's alot better than the one offered on ui.worldofwar.net because it not just download from one site. It is maintained on sourceforge.net and does not contain any malicious code. (I scanned with 3 different anti-virus programs and a anti-spyware one) heres the link if you want to take a look: http://sourceforge.net/projects/wuu
So, armed with that information, I set off to explore WUU.