I put the wrong key in the ignition, now when I put the right key in, the ignition wont turn at all

Try some WD -40 in the key hole. Spray a good bit in to remove any metal deposits.

If the wheels were turned when you last removed the key, that could cause the problem, due to pressure put on the key .
Try turning the wheel left & right while you try to remove the key.
This is a very common problem.
Hope this helps.

Did the wrong key break at all? Check it to make sure its not missing any teeth. How hard did you attempt to turn the ignition before you noticed it was the wrong key?

Its possible the ignition was damaged and you'll need a new one. However its also possible the ignition lock is just stuck and some finagling may get ya going. Try this. Put the key (the correct one :-) ) in the ignition and turn the steering wheel all the way to one side as far as it'll let you. Hold it there and with you're foot on the brake, try to turn the key. If that gets you nowhere, turn the wheel the other direction and repeat. Try this a few times. I had a Chrysler that was particularly prone to this behavior and this got me going every time (though sometimes it took 5 or 6 tries before I hit the sweet spot to unlock it). At no point during this process should you be over straining when trying to turn the key. Keys are more fragile than most people think, and will snap given just the wrong torque, and ignitions with plastic pieces will do the same.

Failing this, if the vehicle has an over-ride switch (little key hole beside the gear selector) try putting your key in there and moving to neutral (FOOT ON THE BRAKE AT ALL TIMES OR YOU'LL ROLL AWAY). Try starting it then. If its a manual, try putting your foot on the clutch and popping the car out of gear. With you foot on both the clutch and the brake, try to turn it again (there's a sensor that can flip out on manuals that won't detect you are out of gear unless the clutch is fully depressed).

If none of that gets you anywhere, I'd expect your ignition is toast...might have damaged a tumbler or two with the other key.

Good Luck! Hope this helps!