When I was at Indiana University, I made it a goal one year to finally figure out how to flutter tongue, and another year how to circular breath. This summer I'm going to finally get my slap tongue up to par with the rest of the Jungle playing cool kids. I've run across these two resources and they've really helped me get pointed in the right direction. Not that I can't slap at all, it's just not that super-picky, ultra fast kind required on many of the newest saxophone works. The first one to check out is this video from the Ellipsos Quartet, and then for something to put on your stand print out this PDF from saxophonist Erik Rönmark.
UPDATE: It took about 3 or 4 months but using the techniques in video and PDF, I am now slapping successfully.