I don't have a truly external pump. I've got an Eheim that can be either submersible or external. It's pretty nice.
If you're looking for an external only pump, then here's my take based on seeing a few and a lot reading on RC:
Poseidon pumps are just about the quietest pumps available. However, they are prone to adding a fair amount of heat to your tank. If you're system can handle the added heat, then they're not bad. I've also read that with their titanium shaft, they can "foul" rather easily -- Ca deposits build up readily -- and need to be cleaned fairly often.
Iwaki pumps are probably the "standby" of the external pump market. They've been used for years and have an excellent reputation. Reliability will probably not be an issue. They won't be as quiet, but you probably won't be annoyed with the noise either.
I'd also suggest that you take a look at the Sequence line of pumps, specifically the Dart or the Snapper. Now, initially you'll probably think that they put out way too much flow, but both can be easily "valved-back" to reduce the flow (and the power consumption). Both are solid pumps. Jay (Dead Beat Reef) has a dart on his tank. It was very quiet, and I could easily put my hand on the pump without fear of getting burned. I was quiet impressed with it and am seriously considering the same pump should I set up my 75g. I'd suggest you get in touch with Jay and see if you can take a look at his Dart. Of course, Dead Beat hasn't posted on RC since the middle of Dec. and I haven't seen him at any of the club meetings lately so I don't know what he's up to ...
DBR -- YOU STILL OUT THERE?
Good luck
