If we're talking top in terms of sales it's probably pretty cut and dried. If we're talking good guns that don't get a lot of ink/pixels and aren't widely known in the US there are quite a few:
Beretta- The PX4 and the Nano are both very good guns that somehow aren't much talked about. The PX4 is pretty interesting and innovative mechanically. My own specimen of the Nano has been superb, rock steady and utterly reliable.
Bersa- Their BP9CC is a great CCW gun. It's slim, light and has one of the better striker triggers I have ever felt. Vastly better than a Glock or S&W in their stock forms. Mine was reliable and easy to shoot. It's a gun that would be popular if more of them sold.
The issue is there aren't a ton of holsters for it and apparently no source of mags except Bersa (best price I have seen was $48 each!). Makes you not feel so bad about the prices of HK mags.
Steyr- Their poly guns are really neat. Same deal, not a lot of holsters or aftermarket accessories. But the trigger is good and the sights are really interesting.
Walther- The PPS and PPQ are both awesome guns, real Glock-killers. The PPQ has about as good a striker-fired trigger as you could want. The PPS is an awesome CCW sized gun. The CCP looks interesting but I don't know much about it beyond the fact that it takes a special take down tool.
HK- I'm a big HK fan as many of you know. I think they make the best polymer guns in the world. They're popular with military clients (the US Navy SEALs use quite a few of their guns) and with European military but not really huge here, so I think it's fair to call them underrated. The USP line is as bombproof and reliable as it gets. The Mk23 is awe inspiring. The P30 series boasts some of the best ergos ever in a sidearm. The P2000sk offers superb reliability in a pretty small package. And the VP9 has about as good a trigger as you will find on a striker gun, about a dead heat with the PPQ.
