I definately second the "fly over the MOB in Nova form and go Dwarf" trick. It's just so satisfying when you THUD! down into the middle of them. 
While fighting in Dwarf form (mainly PB, although I think Warshades knock down too) watch for the foe to be knocked down. Quick form shift to Human to either Essense Drain or Incandescent Strike, then back to Dwarf form. Mire works too.
Shadow Cloak, then Starless Step to bring a Quantum to you, then Gravity Well to hold him down. Beat until dead.
Shadow Step into a group, with Shadow Cloak up, Sunless Mire, THEN Dwarf and Black Dwarf Mire. Not quite as good as Nebulous Form maybe (I'll have to try that) but still catches them off guard.
Heh. Most of these are Warshades. It's the addition of Teleport on top of the other combos, I think.
Kheldians are unique in that many of their strongest combos require them to switch forms. Other combos don't require you to change forms at all.
I've found, however, that I'm not very good at figuring any of them out without lots and lots of debt, which I try to avoid when teaming.
Have a really cool power combo that you use a lot and don't mind sharing? Post it here!
Mine are pretty mundane, I'll bet.
I personally like to use Nova Form in room with high ceilings to drop the Dwarf form directly into a mob. Teleporting into a big group while in Dwarf form is more survivable than some things, but there's still a couple of seconds after 'porting in during which you can't move, which makes positioning harder, and prevents a Peacebringer's Dwarf form from using its White Dwarf Flare PBAoE power at all until you finally touch the ground. Dropping right down from Nova form, after a little practice, lets you land right into a group which has already been partially knocked down by Nova's AoEs, leaving you avalable to taunt, engage in melee, or heal yourself really quick.
I also like to open up in Dwarf form as a Peacebringer, use White Dwarf Flare, and then go into Human form where I use Photon Seekers, with Solar Flare, Incandescent Strike, and Radiant Strike left available for any survivors. I prefer to activate Photon Seekers in the middle of a group because they have a much higher chance of immediately tagging an enemy and exploding for big damage.
On my Warshade, I like using Nebulous Form whenever possible while opening with the Human Form in order to more safely activate powers like Eclipse that draw lots of enemy attention. As a matter of fact, I almost always activate Eclipse like this. Nebulous Form is one of the best survival tools Warshades can have.
Too many alts to list.