I'm having a play with robotics stuff now, and one of the first steps was to get something moving.
I ordered some cheapo servos from ServoShop UK and had a play, they work fine.
However, to use them as easy-to-drive motors for wheels and stuff, you need to modify them to have unlimited rotation (they normally only have 180 degrees). This means they can no longer go to an exact position, but can be driven in different directions and their speed controlled, all through timed pulses - so much easier than wiring a motor, gearbox, H bridge and then controlling all that! (and cheaper, too).
I also photographed each step of the way to make a mini-guide on modifying this specific servo, hopefully this will help out someone with these (fairly common) servos.
Click the picture to go to step one, then step through each photo in Flickr (you can see the thumbnail for the next photo under the Set title):