Mini-Frame by Sqeuieu
This is my favorite frame at the moment. Nearly every piece on the thing can be expanded, changed out, or used for some detailing. It's poseable, looks sweet, and is sturdy to boot.
Sqeuieu has some cool variations in his brickshelf gallery, and (please excuse the self-promotion) I've got a few designs as well. The only real downside to this frame that I can see is that it requires 7 of those four stud 1x1 bricks, which are some of the pricier pieces to buy in large amounts. There is an LDraw file of this guy available on Divnull as well.
Hi-Leg by Joshua AC Newman
These guys are pretty sweet. A very well built and unique frame compared to most of the other guys around. I love the reverse legs and all the potential the torso has. Here's a variation by Jed September that I absolutely love, and here's a company of hi-leg badboys with a commisar by Soren. Aaaaaaand here's the breakdown shot of the torso for all you would be Hi-leggers.
WRH-102 Warhorse by triple_ought
While this one is quite new, I really love how it has the feel of a commisar on steroids. Triple-ought has a few variants as well as a breakdown shot of his build. I can't wait to see what the rest of the community does with this guy.