When someone comes up with a "classic rap" radio format — and it'll surely happen one of these years — you can bet Ice Cube will be in heavy rotation, alongside Bell Biv DeVoe, Mark Morrison, and Sir Mix-a-Lot. Besides having NWA, Westside Connection, and solo hits to his name, there's also the fact that nobody knows how to appeal to multiple generations of rap fans better than Cube. In concert he apes the Rolling Stones, trotting out a hand with two digits crossed in the "westside" salute. Even if Cube's new album Raw Footage tanks, there's no denying he's had his (middle) finger on the pulse of American popular music for more than two decades. Ice Cube performs on Tuesday, Aug. 26, at the Fillmore at 8 p.m. Admission is $46.50; call 346-6000 or visit www.livenation.com.