LensHero launched this week with a tool to simplify selecting a lens for digital SLR camera. You type in your camera model, select a budget and let LensHero select a lens based on style, zoom or your current lens mix.
I upgraded the lenses for my Canon 20D DSLR last month, and I was interested to see how LensHero rated my choices. My Canon EF 17-40mm f/4L USM only rated 7th despite having the exact search parameters I used, and the Tokina 16.5-135mm f/3.5-5.6 AT-X DX Canon-EF rated 6th despite being a poorer lens. The Tokina got higher marks for having a greater zoom range but there is no sharpness rating, which is the weak spot for the Tokina. It also had only two reviewers whilst the Canon lens had been reviewed by over 400 happy buyers (Reviews used are from B&H Photo, one of my favourite retailers)
Entering my current lenses into the suggest function identified the Canon EF 70-200mm f/2.8L IS II USM as the lens I needed, and I agree as it has been on my wish list for several years.
Overall I found that LensHero will present you with suitable lens choices based on your inputs and but it still requires the buyer to assess the data before taking the plunge. If they can incorporate image sharpness into their algorithm, it could became a killer app for lens buyers.