Actually, you may not even need a vps provider yet...how many users are you getting online at one time?
It maybe a waste of money. DreamHost does oversell big time therefore you'll get crappy service. They promise way too much for just so little. Not only does dreamhost does this but hostgator does it too. so it's really sad. For vps i reconmend you try:
IGCHosting, or
NetXservers