Well, for shear variety of engines, you might want to visit the MECOA website:

http://www.mecoa.com

MECOA manufactures and/or sells engines under the MECOA, RJL, K&B, GMS, HP, and HB brands in a wide variety of sizes and configurations.

As the marketplace has been moving more and more toward brushless electrics, the demand for glow engines is weakening. Lines like ASP, MDS, MVVS, Tiger Shark, and others have been getting weeded out of the North American marketplace over the last couple of years.

I'd assume that you're already familiar with the offerings at http://www.towerhobbies.com and http://www.horizonhobby.com. Between those two distributors, you've got O.S. Max, Super Tigre, GMS, Tower Hobbies, Magnum, Thunder Tiger, Evolution, Saito, and Webra represented, although Tower doesn't carry full lines for either Thunder Tiger or Magnum. You can look at http://www.infinitehobbies.com for a complete line of Thunder Tiger engines and visit http://www.hobbypeople.net for a full line of Magnum engines. Hobby People is also selling the Mark line of engines by Moki.

If you're interested in Norvel or Aviatech/Aviastar engines, you can find those at the http://www.sigmfg.com website. Sig is selling the Norvel AX-40 for $59.99, which seems like a very solid value. You will want to visit http://www.centralhobbies.com for a fairly complete listing of YS Engines.

I believe I've covered most of the 2-stroke and 4-stroke engine lines available in North America. I didn't venture into Gas power with the above listings. Hopefully a couple of other posters can fill in some blanks for you.