Sources: File hosting servers for Cydia applications.
Add a Cydia Source
Open Cydia > Manage (tab at bottom) > Sources > Edit (top right) > Add (top left)
Standard Cydia Sources (as of 7/31/2012):
BigBoss, Cydia/Telesphoreo, Dev Team, ModMyi.com, ZodTTD & MacCiti.
My Cydia Sources (as of 7/31/2012):
Hackulo.us: (http://cydia.hackulo.us)
insanelyi Repository: (http://repo.insanelyi.com/)
SiNfuL iPhone Repo: (http://sinfuliphonerepo.com/)
xSellize:http://cydia.xsellize.com/