Takashi Mobile MVNO/SP List - out of date

Includes most prepaid providers: 7-Eleven Speak Out (Ztar, Cingular), Boost Mobile (Nextel), Call Plus (AT&T/Cingular), Locus (AT&T), Page Plus (Verizon), Tracfone (Cingular, Verizon), Virgin Mobile (Sprint). 

7-11 speakout canada 
Takashi Mobile MVNO/SP List (updated list of MVNOs and Mobile Service Providers World-Wide) old
Second source from cellular-news MVNO/MVNE 2006