Winning isn't everything, but losing just might be. In fact, coming in second has been a career booster for some high-profile losers who by rights should be on the trash heap of also-ran-dom. Take ''American Idol'''s Clay Aiken. Not only did the angel-faced crooner's second-place performance land him on the cover of ''Rolling Stone'' before AI winner Ruben Studdard, but his debut CD, ''Measure of a Man,'' sold a commanding 613,000 copies in its first week of release (Studdard's hits Dec. 9). ''I almost feel like the fact that he ended up being a runner-up kind of added to his appeal,'' notes ''Billboard'''s Geoff Mayfield. No doubt that idea is what prompted the folks behind ''The Bachelor'' to cast unlucky-in-made-for-TV-love runner-up Trista Rehn. Then there's ''Bachelorette'' reject Bob Guiney, perhaps the most lovable (turned kiss-happy) loser making hay on the small screen. Hey, in a country where not actually winning the popular vote can lead to the Oval Office, it pays to aim low.