Radiohead, The Smashing Pumpkins, Metallica, and Jane's Addiction each had great album-opening rock songs in the 1990s with iconic riffs.
Many guitarists have favored drop D to add thickness to their riffs. The list would include Eddie Van Halen, Jimmy Page, Kurt Cobain, Kim Thayil, Jerry Cantrell, Dimebag Darrell, Tom Morello, Adam ...