It's been so long since I've been on the forums, but anyways....
Hitmontop @ Assault Vest
EVs: 252 HP / 252 Atk / 4 Def
- Rapid Spin
- High Jump Kick
- Stone Edge/Earthquake
- Sucker Punch
This is my personal favorite user of Assault Vest. With good 50/95/110 defenses combined with what's essentially a +1 defense and special defense (if you're switching in and the opponent doesn't switch out), Hitmontop is able to tank several hits. High Jump Kick is used over Close Combat because Close Combat lowers his defenses, which is not recommended with a set that relys on its tankiness. Stone Edge may be used to catch Gengar and/or a flying type on the switch in, while Earthquake is super effective on Mega Gengar and Aegislash, two popular spinblockers in the game. Finally, Sucker Punch is that useful priority move for Hitmontop.
Other nice users of Assault Vest are Regirock (who has an obscene 200 defense and 100 special defense to abuse, as well as a good 100 attack. A set with Drain Punch, Stone Edge, Earthquake, and Explosion could work), Scrafty (with Intimidate and great defenses), and Cobalion (Assault Vest covers its bad 72 special defense. It also has Volt Switch to escape from anything it doesn't like).