i would suggest gerbils cos they come in lots of different colours most of them on this site:
and they don't use the toilet alot so their cages can stay clean for up to 2 -3 weeks for me.
They are also VERY friendly cos my gerbils go EVERYWHERE with me eg.shops, park,in my bed etc. They LOVE to get out of their cages and have fun cos otherwise they get bored. They like rats and mice very social so you need more than one.
They rarely bite and if they do it means most of the time that they are really angry or in great pain.