If you can't afford Michelin's 'real' rain tires, http://forums.mra-racing.org/viewtopic.php?t=11084, I've got a set of Michelin Pilot Power 2CT street tires with additional grooving.

I got these at our second MPH visit, had 'em mounted, and never had to use them - they are that good. List is around $300 I think, they are your's for $150.