You could always teach your cats how to defecate in the toilet. (don't teach them how to flush though as they will continually flush to the chagrin of your water bill and mother nature.)
The latter part of your post is largely why we didn't go with this option, although it would be nice if they could take care of their waste themselves.
Not all at the same time, I grew up with cats, dogs, iguanas, fish, ferrets, hamsters and rabbits. By far for me cats have been the most worthwhile investment. Dealing with the small inconvenience of the litter box is something I shouldn't complain about since simply having my cats around for companionship has paid off such valuable dividends.
