The only ones out there that I know of are made by Hydor. Quite frankly hydor is not exactly a high end brand. When I set up my cichlid tank (which has a canister) I considered them but I just couldn't trust a heater made of more plastic than anything else, so I went with a standard submersible.
If you can find them, Aquanetics used to make an awesome inline heater called the fireplug. They don't make them anymore, but you may be able to find a used one with enough hunting around.