I agree with the majority here, we can hardly go recommending another pet, not knowing why the kitty had been given up, that is kinda irresponsible IMO, and besides she asked our opinions.

One should never get another pet having given one up unless there is a very genuine good reason.

However if there were some good reasons, perhaps mice would be the easiest pet I can think of to take care of ,time wise, money-wise etc.