A friend of mine had a toy poodle that was litter trained-she used a litter box just like a cat! I also really like Wheaten terriers but they can be stubborn and may be larger than what you are looking for (about 30-30 pounds, I think), Papillions are very cute and I have heard good things about Cavalier King Charles Spaniels as well. I also know a pug/Boston terrier cross who is very cute. Shetland Sheepdogs need a fair bit of grooming, but are supposed to be very sweet.