I used to have this problem all the time. Depending on the situation I will try a number of things. First would be to try a De-sser. If that doesnt work, I try to convince the drummer to do a couple things. (1) Raise the hats up, and (2) move the top hat down (in open position) so they dont ring for so long. Most drummers who have this problem dont understand that having your hats 3 inches apart (when open) isnt a good idea, in most practical applications. I also have a pair of dark, 12" cocktail hats that I keep around. For fast music I find that they work really really well. They sound silly when they are way open, so they only work with drummers who are ok with their "open" sound a little less bombastic than usual. At first with the drums isolated they sound funny, almost like the hats you find on a shitty drum machine, but once you adjust, and start adding insturments, they are amazing. The tight "chk" sound still cuts through perfectly, but there is not all that other washy shit to eat frequencies and cover your snare. They dont work in all cases, but when they work, they are perfect. The ones I have are made by Po-Boy. They were dirt cheap on ebay.
Cocktail hats - get into it.
You can them on my bands myspace
www.myspace.com/youngbelieversma
These are rough mixes, but youll get the idea!
Let me know what you think!