Here's three I use:
Focus sash + Destiny Bond
Focus sash on a Timid Gengar that knows Destiny Bond is deadly. Cheap but deadly. :D Timid means it'll be fast, which it needs to be fast so it can use destiny bond just before it is killed. Here's what you do:
1st turn: "Free" turn, meaning you are usually safe to try your luck at KOing (unless of course the opponent is faster, like Aerodactyl, or uses Fake out, ect.)
2nd turn: Depending on how much damage you've done in turn one, and you're still alive thanks to focus sash, you can now try to 2HKO. If you can't, use Destiny Bond. This is a really good strategy to use in the Battle Tower. In most cases, you will KO at least one of the NPCs pokemon by the time Gengar goes down. That leaves you with only two more to deal with.
Swords Dance + Bullet Punch
This is the classic set up executed by Scizor, since Scizor is by far the best at it. It's simple: Scizor uses Swords Dance, but it is outran by the opponent. Suddenly, Scizor attacks immediately afterward because bullet punch is a priority move, and BAM, dead pokemon. After a 200% increase from Swords Dance, a 130% increase from Life Orb, another 150% from STAB, yet
another 150% from Technician, and a possible 200% if it is super-effective (critical hits anyone?), suddenly that base 40 attack becomes monsterous.
Wish + Protect
IMO Vaporeon is the best at pulling this off. Wish takes two turns, right? Well since Vaporeon is (like Scizor) kinda slow it can use wish after the opponent, and then immediately throw up protect to avoid damage, then wish hits. This becomes extremely frustrating for opponents if Toxic is thrown into the mix.