#1: The puzzle combat. This is a classic. The PCs are engaged in a combat that is extremely difficult for them or that they can't finish. Something where the enemy doesn't do a whole lot of damage per round, but will take a very long time to kill works, or something like skeletons that keep rising every time they're destroyed. The object is for the PCs to realize that they can end the combat through doing something besides hack and slashing.
#2: The trapped room. Combat in this case takes place in a room filled with traps, moving parts, or other such devices that make the PCs have to work together to accomplish without much hardship. Perhaps the party fights while the rogue disarms a trap or one character must hit a lever that allows another character through a doorway, or a strong character must hold a chain down to keep a bridge from falling. Be creative!
#3: Get the MacGuffin! Killing the enemy isn't the primary goal. They have something you want, and you need it now to do something. Disarm them, grapple them, hold person them. Do whatever it takes so that you can get the scepter and put it in the slot, or get the orb that is summoning a powerful outsider and smash it!
#4: Hostage? One enemy is slowly escaping with a hostage while two others engage the PCs! What do they do? Saving the hostage is the first priority, but its being made very difficult by the situation. If they all stay and fight the two enemies, then the other guy will get away. They need to think of something and pull it off -- fast!
#5: Charmed villiagers! A vampire or some other creature is using innocents against them. They need to break the spell, convince the villiagers that they aren't a threat, or find some other way of dealing with the threat before they themselves are dead.
#6: Three way battle? Who's on who's side here? The PCs engage with enemies who are not only fighting the PCs but they're fighting each other! Is it a case of mistaken identity? Are some of them actually allies who don't realize it? Can the PCs form a temperary alliance with one group to crush the other? What happens after the first group is crushed? Should the PCs back off and see if the two groups kill each other? Why are they fighting in the first place?
#7: But... he's good! Mistaken identity or miscommunication can be a real pain, especially when the local clerics of Pelor believe you're assassins. Perhaps its time to beat a hasty retreat, or maybe nonlethal combat options are in order if you can pull it off. Maybe diplomacy will work if you're good enough. Whatever the case, you best not kill them because if you do, you'll have some real crimes to answer for.
#8: Goad them. Nothing says "roleplay" like PCs getting insulted every which way, and few can take it. Make the NPCs yell out at the PCs, whether its about how horribly the fighter wields his sword, insults to the cleric's god, or laughing at barbarian's loincloth, the PCs will not like it one little bit. Encourage them to shout back, and make the combat about insults as well as survival.
#9: Barrom Brawl. This is a true classic of D&D combat. It's usually nonlethal, but the problem is it usually serves no purpose, its the barbarian going out and punching a random guy in a bar. Give it purpose! Make them have a reason to start trouble in a bar, and make an NPC throw the first punch! They run into their arch-enemy in a bar (had that happen in a campaign, it was awesome), someone they slighted runs into them (ala the Gamers), there are just so many reasons for drunk people to fight, you'll think of something!
#10: The PCs are the Law. When the PCs have to arrest someone, not kill them, then things get more complex. They have to subdue them, manacle them, knock them out, diplomacy them into submission!
#11: Props, props, props. Chandaleirs, carpets, tapestries, banasters, stairs, slopes, doors, dumwaiters, bridges, spikes, tables, chairs, rocks, trees, ladders, nooks & crannies, two foot holes, book shelves, alchemist supplies, fire, anvils, frozen ponds, vines, quicksand, cows, trophies/candlesticks, secret passageways, beds, cramped spaces, barrels of grog, wetbars, muck filled pools, stalagmites/tites, clock tower gears, wagons, fire rain, waterfalls, etc. Be creative. If you build it, they will use it.