I always thought guinea pigs were just overgrown hamsters until we got our first one a few years ago. They have a lot of personality, actually. They do not bite unless they are under extreme stress so are gentle for young children. They do poop a lot, just like rabbits but it is very small and easy cleanup. They require vitamin C and will eat fruits and vegetables.
We have had our most recent pair since late 2008. We adopted them from a family who were unable to take care of them due to the unexpected death of the young father/husband.
The gray one has been sick for a while. Multiple trips to the vet have not cured whatever its ailment was and she continued to decline until this week when we had to euthanize her. Now we are working on getting another one. Callie is the caretaker for them and misses the gray one (named Kyoko) very much. The remaining guinea pig also misses her – piggies are very social animals. I am talking with a foster mom about a couple of different ones that might work for us. We prefer to adopt a rescued piggy than to use a pet store.