I love pololu. They test their stuff before they sell it, and they support it in their forums. I am a happy customer of theirs.
The reason they are not as cheap as the Chinese direct sellers, is that they actually do test their stuff, and they actually do support their stuff. That means they have to pay more salaries, which means they need a larger margin. I wouldn't call them "expensive" by any stretch of the imagination, though -- the same performance gear bought from a commercial motion control company would cost between 2x and 10x as much!
I've used their 37D gearmotors with encoders, and they perform as advertised. I've also used their micro metal gearmotors, and they also perform as advertised, although the warning about not soldering contacts for too long is not kidding -- the plastic melts easily and ruins the placement of the brush on the inside of that contact. (I found this out trying to de-solder from it.)
I also really like their pre-crimped wire/cable harnesses, and their switching voltage regulators, and their motor controllers (H bridges.)