Can I buy a prepaid sim card in California to use with my unlocked Samsung i600 (blackjack) mobile phone?

I live in Vietnam and am traveling for a month in the US (California). I have a blackjack, Samsung i600 in Vietnam. Can I buy a prepaid sim card, so I can use it in the US without a contract? Which carrier has the best deals? What should I expect to spend? Any thoughts on high speed data access would be welcome as well. Thanks