I prefer slotteds. That's a personal thing I guess, but I go into my theories on it in our Project 854R. We have Powerslots from IPD, but I think there are other slotted choices out there and Kai knows a guy who'll do it to a regular set of rotors.
Check out Eurosport Tuning as well, I think that they have some great products. The might have some holiday deals going on as well. Like the others have mentioned, I would go with slotted rotors over cross-drilled.
If you are serious about buying the cross-drilled rotors, I would highly recommend sending them to http://www.frozenrotors.com prior to installing them. My father had cross-drilled rotors on his XR4Ti & had stress cracks at the holes within a year of use.
Just something to look into.
I have installed the drilled and slotted rotors as found on eurosporttuning. I drive the car VERY HARD as well as have 6K+ miles on the brake job. By this time with the OEM setup I had vibrations! I used the OEM pads from Volvo as well as their silicone goo and additional rear pad shims. The brakes are solid and feel better than most of the LMSC NASCAR cars I messed with in the past. The price is good as is the fact that the parts are not too far out of OEM spec. It allows you to sleep better at night knowing that the OEM base was used along with the DOT approval and quality standards. Brakes are no-joke. Don't play around with them too much.