For a return, you will want between 3 and 5 times total volume, for a 120, you're looking at between 500-700gph give or take a bit. For an in sump, submerged, pump I would recommend the Eheim 1260 or 1262. Its reliable, quiet, low energy consumption and does not transfer heat.
You're other options would be a Mag 5 or 7 which are louder, transfer more heat, use more energy and can have restart issues. A quietone would be an option as well, but the reports of the newer models are not as reliable as the older versions having restart issues.
You can get them online at MarineDepot.com or PremiumAquatics.com and get them fast shipped... or call around to your LFS's and see if they carry any of them.
