Waterfall and Surf, depending on whether the pokemon who's going to get it has better physical or special attack.
I can tolerate Strength, and used to use it a fair amount on Normals before the 5th gen, since TMs weren't reusable. With Reusable TMs though, anyone who might've gotten Strength gets Return instead and Strength just goes on a slave. Rock Smash can be useful occasionally, since it's the only Fighting move that a lot of non-Fighters can get, but it just doesn't do enough damage, and they're generally better off with neutral STAB over even a super-effective, off-type base 40 move. I've never liked Fly, so it's always gone on a slave. Even though the AI won't take the opportunity to switch out, it's still two turns of passive damage, paralysis checks and accuracy checks just to get off one turn of damage.