Great recommendations so far.
If you're wanting to catch lightning, your looking more at tripod work and timed exposures. Once lightning flashes, you can't just start snapping away and hope to catch some good shots (you probably know this already). If you're doing nighttime lightning shots, your looking at timed shots with wide open apertures.
What I find amazing is you can take thousands of pics on some of the flash memory cards, and preview all of them, delete the bad ones, and keep on shooting. In the 'bad ol days' of film, I'd take maybe a roll, of a storm rolling through, and even 'knowing' what I was doing, more than half would be worthless.
Outside of the fps, any quality digital camera will work.
With a dslr, with a fast fps, you're probably looking at lower resolution shots... I don't believe many of the dslr's will do fast fps shots in RAW resolution... the images are around ~20mb, which would fill up most memory cards in a hurry. A gig card would hold only 50 shots......
Let us know how the storm chasing works out... always thought I'd like to do that someday... my knees are getting shot, and rock climbing doesn't work too good for this body of mine...