Just came across a couple of interesting kettlebell swing variations on Pavel Fitness (that's Joe Pavel, not Pavel Tsatsouline). The first of these is used as a training aid, and is a great way to ensure that your hips are doing the work, rather than your arms. The bell isn't being lifted, it's being swung.
This is done by taking the arms completely out of the equation. Tie a rope to the bell, loop the other end around your back (the rope should be long enough to let the bell hang around knee height at the start) and thrust away. It's probably best not to do this one in a busy gym (unless you're ready for the comments).
Kettlebell golf swing
The second exercise is the Kettlebell Golf Swing. Standing with knees slightly bent, hold the bell with both hands (via the handle) and swing it in front of your body from side to side (not too high - you're putting here, not teeing off). Initiate the swing with your hips, and move your knees in the same direction as the bell. Pavel's video (8.26mb) demonstrates this clearly.
As with the other swing variations, this is great as part of a warmup.