So cool: Sephora.com has a fragrance finder, where you can choose a scent you like and it will recommend other scents that are similar.
It's not 100% accurate though. I love Dolce & Gabbana Light Blue, and I don't think it smells anything like the grapefruity-but-too-sweet Escada Rockin' Rio (which I almost did buy) and Fleurs des Caraibes. It gave me some better recommendations for Fendi, though -- I really do like the Prada scent.
Also, it isn't comprehensive. I tried to look up Kenneth Cole Black, which Rob loves, and didn't see it even listed. Which is weird, since I know Sephora sells it.