Lenses are one thing that most budding photographers don't understand. Megapixels and all that are fine, but put a 50mm in front of them and start talking about F-stops and all that and you've lost most of them, including me.
LensPlay is a database of mostly Canon EOS lenses and there are a few basic query functions to drill down to the one lens you're looking for. You also get reviews, ratings, and price information as well as all of the specs. One ideal feature would be an example of a scene shot with that lens, but that might be a bit too convoluted.