We used several methods, all of which mostly worked, though what really helped was age...our 12+ year old cats just aren't interested in jumping so much!
In order of effectiveness for my cats, though we used all of these at one time or another:
1) Use a water pistol, not a squirt bottle, especially a mister. You can get good range, and the stream really seems to annoy/startle them. It's also best if you can do it surreptitiously so they're not sure *where* the water came from. Walgreen's usually has water pistols in the $1.00 range...buy several and keep them located strategically around the house/apartment.
2) Balance cookie sheets on the edge of the counters, so that when they jump up, they unbalance and fall down. This is especially effective if either you have hard floors (lots of noise) or you put some pie plates on the counter side of the cookie sheet (lots of noise).
3) Get some of that clear vinyl carpet runner (like my grandma used to have!) and turn it upside down on the countertops, so the little spikes that hold it in the carpet are facing up. They're not sharp enough to hurt the kitties' paws, but they certainly annoy them. You can find this stuff in rolls at Home Depot or Lowe's.
4) The tinfoil thing kejoda mentioned works too--especially if you accordian-fold it before laying it on the counter--this seems to really bother them.
Good luck!
=joye