Although in the world of MVNO's, there are more prepaid CDMA than GSM compaines with in America. Providers are finally waking up, some companies not allot are starting to offer a "Starter sim pack"

Clear GSM clear gsm

Xtreme Mobile xtreme mobile

Hop on hop on

are three examples I have come across for now.

??? Can anybody come up with others ???

All these seem to be "coming soon" (in two cases, on dates in the past!). None of them seem to be active, although maybe they are just concentrating on dealer recruitment so far.

THese MVNOs are growing like mushrooms!

Here's another one:
http://www.coolprepaid.com/

cool prepaid is a new one for me.I also found these graffiti prepaid although the website is not up yet. & .GTC Telecom ,TuYo Mobile, VOCE (luxury class MVNO)
thanks for adding to the list

Here is a canadian GSM MVNO:
http://www.m-mobile.ca/canada/en/index.html
They look affialiated with SiM Pro but they seem to resell in the same fashion as them though :)