Forgive us for assuming Rihanna was a one-hit wonder. After the 18-year-old’s reggae-inflected debut, ”PON DE REPLAY,” blared from car stereos last summer, we figured we’d heard the last of her. But the Barbados native is proving that pop lightning does strike twice. And this time, she’s traded the Caribbean flavor for a more northern inspiration: Her buoyant No. 1 hit ”SOS,” driven by a heady sample from British new-wavers Soft Cell’s 1982 gem ”Tainted love,” is shaping up as the summer jam of 2006. Even Rihanna finds it bizarre that she’s reviving a beloved classic that first landed in the top 10 nearly six years before her birth. ”Oh, my gosh. It’s crazy, right?” she giggles in her lilting, just-perceptible accent. Discovered by producer Evan Rogers in 2003, the singer blossomed under the tutelage of Def Jam’s current head, multiplatinum hip-hop star Jay-Z. Next up? A summer tour and a second single, the ballad ”Unfaithful,” which is already climbing the charts. We would be more contrite?but we’re too busy swaying to the seductive beat.