I find most cats are pretty easy to train to a sound. It could be a finger snap, the squirt of a spray bottle, a clap of the hands, etc.
The key is to be consistent about it, and only use the sound when they're actually being bad. In addition, try not to let them associate the sound with you, or they'll only be good when you're around.
Initial training is often done accompanied by an action the cat does not like. I usually use a spray bottle since our cats hate getting wet and its easier to hide the fact that I am responsible for the action. I find that a loud noise or a hiss will startle them and work as well, although it is harder to prevent them from associating the human-made sound with me.
I actually had the same problem as you where we had one cat that would always be jumping on the counter when we weren't in the room. As a solution, I lined the edge of the counter in empty pop bottles, and after scaring herself twice by knocking them all down, I haven't caught her up there again. I've heard people report the same sort of success with using tin foil or something sticky like double-sided tape on the counter, however that never worked for me (Tinfoil = Toy, and Sticky Stuff = Annoyance) :)
Zaralynda's answerZaralynda's answer does provide some good advice too about trying to find and fix the reason for the cat's behavioral problems, however since this question is specifically about how to discipline a cat, I figured I'd provide an answer that addresses that.
Cats can be just as trainable as dogs, although I find it harder to do since they are usually more independent and not as eager-to-please as dogs, and are sometimes smarter than dogs so can figure out what you're trying to do and choose to ignore you. :)