What's a good workout that will make me muscular, but keep me slim?

I'm trying to get more toned and cat, but at the same time without adding a lot of bulk. I already swim about 1000 yards a day, and run 6 miles every other day. I'm wary on the weights, as I don't think the bodybuilder look would fit well with my frame. Any workout schedules/tips/exercises would be greatly appreciated!