One of the things I like about WoW is finding new, unusual ways to use old skills. For instance, I recently observed a bear druid using Feral Faerie Fire on critters. When I asked him why, he responded that it keeps him in combat, preventing rage decay. It's a very clever tactic, and one I'll be using once I get my druid high enough for it (then again, I'll probably be in cat form most of the time by then). Another classic off-schedule use is Detect Magic as a marker ("attack this mob" or whatever), though that's largely been eclipsed by raid markers. And speaking of raid markers, they're quite useful even when solo, since you can see them through walls.
What are you favorite unusual uses for skills or features?