I know that Guinea pigs do best in pairs. Other than that I have no idea. Personally I would go with a hamster since they are alot easier to take care of than guinea pigs.
If you want more info from experts (which would not be me!), go to
http://www.petfinder.com/messageboard
Its made up of all type of pet owners and animal lovers. There are many people on there that are quite knowledgeable and would love to help you out!