As you may imagine, the cymbals that came with my new $20 drum set were pretty gross. Normally I don't bother to clean cymbals (in fact many advise against it) but the black mold and weird sticky spots were a little too much, so I decided to try cleaning them with stuff I had laying around. I took some lemons, a little white vinegar, an old sponge, and some extremely fine sandpaper and got some pretty impressive results after about a half hour of work.
Soak the lemon juice into the sponge and work it into the grooves really well. Rinse with warm water and repeat with vinegar. Dry the cymbal thoroughly as the last step. I used tiny-grained sandpaper but you might want to avoid this to preserve logos or if your cymbals have a particular coating. All of the cymbals that came with my set were mismatched, but each cymbal manufacturer makes a specific product for cleaning their wares. Don't blame me if you mess up your overpriced boutique china crash!