I would strongly advise AGAINST using an undergravel filter for anything.

Anyone who has ever broken down an established aquarium that has run an undergravel filter for any extended period of time should know what I mean.

The amount of waste that gets pulled under the plates that you will NEVER get out during cleaning is amazing. I can't believe that something could live in a system like that.

I've had great results using Aqua-Clear Hang-ons and Eheim canisters.

Also don't forget about circulation. If you have a well-stocked tank, it helps a lot to have a strong powerhead in the tank moving the water around to prevent any dead spots and allow your filter to efficiently grab all of the waste.

And like Gin said, most of the successful fishkeepers I know overfilter their tank...shoot for a filter that moves enough water to completely turn over the tank 3-4 times an hour.