Here are the list of open source project I am learning from and have been part of :
Socialtext OPEN Been a user of this for a couple of years now.
WordPress Started wordpress.com and now have own local and online install i.e. this blog.
Drupal: Got this install but still struggling to customise
Clamwin: I use for anti virus
And Elgg, an open source social network, people aggregator are opensource too but I have not looked at their code.
So, I need a place on sourceforge.net and website/wiki to host code, build, manage project etc.