Here's what I have already: 400D w/grip Tamron 17-50mm f/2.8 Canon EF 70-200mm f/4L Canon EF 50mm f/1.8 I know I would use it a lot because I love wide angle photos, indoors and out. But I'm worried that it will be too slow to take pictures indoors without a flash (don't own one). I've looked at the Sigma 10-20mm as well, but it's hard to find a place with a good price here (Bangkok). The guy at the camera shop today said they don't sell them anymore because they've had a few defective ones. One customer's camera would show an error message sporadically when using it. Is it worth the $680? Should I keep trying to find a good price on the Sigma?