Most people use windshield washer pumps from cars.
We are making up our own pumps from a discarded pump housing.
The mounts will fit a standard RC car motor. From preliminary tests, the pump will be able to move about three gallons a minute. We are going to run two to three of these in [link=http://www.rcgroups.com/forums/showthread.php?t=77749&page=1&pp=15]models of the LA Fireboat #2.[/link]
There was quite a bit of machining to make the necessary adaptations for the impeller mounting and water seal, but we are confident that the pumps will be able to move up to 350 gallons an hour. Of course by that time the motors will probably have overheated.
The second image is a jet pump design. As designed, the two intakes should be able to supply enough water to create a 60mph jet of water. The force should give us a 20mph boat.