For those who can not know the "sources" are, here are some explanations about the sources for iPhone 2.0 users. Source network address, or add applications, cydia installer download. More applications can be downloaded from the addition of new sources. Different things different host sources, such as applications, themes, wallpapers, art, etc.
Most applications are available at the source (usually a trusted and pre-installed), but others do not, and need to add manually.
You can manually add the list:
app.ifonetec.com: http://app.ifonetec.com/cydia/
cake.mapleidea.com: http://cake.mapleidea.com/cydia/
BigBoss & Planet-iPhones: http://apt.bigboss.us.com/repofiles/cydia/
Hack & Dev.org: http://iphone.hackndev.org/apt/
Hackers.nl: http://apt.hackers.nl/
iClarified: http://cydia.iclarified.com/
iPhone notes.de Repo: http://apt.iphone-storage.de/
ispaziorepo.com: http://ispaziorepo.com/cydia/apt/