1. Throw it away!
Accept the fact that it is dead and gone. There is nothing you can do.

2. Ask the dealer/manufacturer for a replacement.
Try to send it straight back to the dealer or even the cymbal manufacturer. At least try to get a new one before going into major surgery. For example, Zildjian's usually very good about replacing cracked cymbals, no questions asked.

3. Fix with epoxy
Cracked cymbals can be brought back to usefulness. The proceedure works like this. Force Epoxy into the crack. Strike the cymbal hard several times to vibrate glue deeper into the crack. Apply more Epoxy and strike several times again. Wipe away excess. Bake the cymbal in a 200 degree oven for about an hour. This hardens the Epoxy to a glassy consistancy. Let the cymbal cool naturally. Let stand for at least 24 hrs before playing. If done correctly, it works.

4. Fix by soldering/welding
An alternative way is to solder over the crack on both sides (standard solder for electronics). Polish the damaged part until it is all clean and shiny, this way the solder will grip properly. I found this to restore much of the original sound. Unfortunately, it tends to crack up again after about a day's playing (that is for cracks on the edge). I guess that stronger stuff (like welding) might last longer, but would probably melt the cymbal.

5. Fix by drilling
Cracked cymbals are no too easy to fix or work with. You may try drilling a small hole at each end of the crack to prevent further spread, and then widen the crack -- Like they did with the Liberty Bell the first few times it cracked. This will stop it from buzzing, but not much else.
If the crack starts from the edge, drill the other end and then make a wide, V-shaped notch starting from the hole.
Drilling may (with good luck) prevent the crack from getting bigger but it seldom improves the quality of the sound.

6. Fix by turning in the lathe
If the crack is on the outer edge and it's not too deep (towards the center), you can cut the cymbal smaller in the diameter. Of course, turning is likely to change the sound characteristics...

7. Make an effect cymbal out of it
Forget the old sound and try to figure out how you can get totally new, exciting, weird, previously unheard, nice sounding special effects out of it. You might try cutting the cymbal into a new size/shape. For example, just the cup of a large-cupped ride makes a cool bell.