This is a great brand. It's got sensors that can tell when your cat has left the litter box, and it will rake away the waste 10 minutes afterward. This gives the cat time to do its thing and makes sure it won't be frightened while it's in there. The timer will reset if the cat comes back in, and it's got a safety thing so that it stops raking the litter if it hits anything. It's also got a little ramp on it to clean off the cat's paws as it leaves.

Littersweep - This is available here for $79.99. This is a circular one that will rake clumps into a little bin for storage. It's got a waste-based sensor to tell when the cat leaves, and it will wait 25 minutes for the litter to clump up. It has gotten some bad review though from a lot of people who say it tends to jam and can't handle more than one cat. My gut says you should probably take the price hit and go with the Littermaid, but if you want to try the cheaper one, just know you'll get less in the quality department.

Omega Paw Self-Cleaning Litterbox - This one is available online for $32.99. Just be aware this is not really an "automatic" one. It's manually operated - once a day you have to roll the box, which causes the clumps to go into a collection area. But a lot of people seem to like it. It won't do all the work for you - but it does get rid of the nasty scooping part of litter cleaning. And it's very cheap for what it does.