I was / am looking for the Sigma 10-20 and 30 mm 1.4 lenses for my Canon 40d and came across the following on Ebay. It is a set of warnings and info about buying cameras and lenses.
eBay.co.uk - For Digital SLR, Camera Lenses, Photography Reviews & Guides
I thought the one about Nikon lenses guarantees was very interesting if you have one of those. I had not seen this before so I thought I would pass it on.