External, I'm assuming? I have two reeflos dart/snapper I like. They seem to be the best bang for your buck as far as output versus power consumption goes. The only bad thing is the seals will eventually wear out and have to be replaced. Relatively simple and cheap to do, but is inconveniencing because it starts to drip by the shaft when they go and if you don't have seals on hand you may have a few days wait to get them (*hint hint* LFS should carry these!). I try to keep a set on hand when I am using these pumps. I didn't get to use the pumps I have for long, but I was happy with them when they were running. Newer ones are a lot quieter. Plus they have great customer service, that guy (Chris I think?) will go out of his way to help you. They do output a lot though, so I guess that is something to consider as well.