You could try to put a dab of super glue on the key and sticking it in the ignition switch, to see if you can get the other half to stick to it, so you could pull it out.
You may be able to do the method that capt describes (I don't know, since I've never had to do it).
If neither of those methods work, you'll have to remove the ignition swith. Which entails removing the steering column cover, the steering wheel, the multi-function switch (turn signal and headlight switch assembly). Then you'll have to use a chisel and hammer to turn the round headed bolts that hold the key switch to the steering column and remove the switch assembly.