I bought a Canon EOS 40D recently and am looking to start out with an all purpose lens that will get me nice, sharp photos. I've got my eye on the Tamron SP AF17-50mm F/2.8 Di II LD. It's interesting in the sense that it can maintain f/2.8 throughout all focal lengths. It's got great reviews and seems like a great lens ($420). Any other suggestions are welcome. The lens must be at least 17mm as I'll need something for wide shots. Upper range can be anywhere from 50-80mm. Thanks!