The links worked, and are really great info. Thanks for steering me to them!
A sledgehammer is out; I live in an apartment. I do have a bodybar, though, which is 18 lbs and, I dunno, over 4 feet long I guess, which I can swing and, depending where I hold it, it can put a huge strain on my wrists. I practice various simple martial arts staff moves with it sometimes, which is what I bought it for, and holding it off center really magnifies the weight, and so does moving it with some speed. Catching the momentum you generate can be a work-out.
I just got my kettlebell two days ago, but have been doing some swings and just general shoulder work with a dumbbell to get myself a little used to the exercises before it came. Now that I have it, I really like it a lot more than a dumbbell. The grip is very thick, and the off-center balance means that I can effectively vary how hard it is to move around quite a bit by how I hold it.
I really like the swings and the "windmill" exercise that kettlebellers do. It's tricky, works and stretches your body in a weird way, and makes you concentrate a lot on stability while you do it. It's just frankly kind of fun to work with, because you're learning and practicing a skill, not just mindlessly grinding out a repetition like you do with regular, balanced weights. I've never found weight lifting fun, I guess because doing the same moves in the same direction all the time just lacks variety and seems so specific to getting better at just doing more of the same. But I get kind of a kick out of the kettlebell. I think I'll probably be getting pretty seriously into kettlebells.
Swings are fun too. With proper form, on them, you really use your hips a lot, and your glutes and the very tops of your thighs. As with any off-balance piece of equipment, though, you can always change your form to emphasize different muscles or make things much harder or easier, which I really like a lot. I like the swings, improperly done, as a shoulder exercise, too, though you can tear something pretty easily if you're not extremely focussed.
All in all, it's a pretty fun thing.
Here's a link to a kettlebell trainer/martial artist's DVD in which he shows some unusual kettlebell drills. There are samples on the page. The duck walk & press and the creepdown & press are cool, and the towel swinging business is very cool.
http://www.fullkontact.com/dvd2.html