A few weeks a go I came up with a new method of building quad walkers. I think I discovered it while sorting. At this point I don't remember so I could be wrong. I feel the torso area of the model in the picture is still incomplete. I have an idea of the piece I would like to add, but I haven't opened the set it comes from yet. Right now the Inverted Slope 45 Deg. 2x2 could be considered the "face" of the frame.
The frame design starts with the Technic Knob Wheel as the core with four of Modified Plate 1x2 w/Arm Up forming the starting point for each leg.
The torso is then mounted via a Technic 1/2 Pin w/2L Bar Extension and a Technic Brick 1x2 w/Hole. The only problem with this is that you either have to leave the space above the brick empty or mount another one on the exposed stud.
This does give you a place to mount future attachments though.
If you place a Technic 1/2 Bushing on the bar section between the Knob Wheel and the Brick w/Hole, you can lift the torso up a little so it doesn't ride so low.
Hinge Plates to form the "knee" portion of the leg. You can use multiple Modified Plate 1x2 w/Handle on End and a Modified Plate 1x2 w/Clips Horizontal to make a couple of legs.
I only have two and a half of these built so I'm still exploring options right now. Quad 1 Flickr page. Quad 2 Flickr page.