If you are shooting Canon and want a true USM lens you have limited options. The 17-35 2.8 USM is very pricey and has a few major shortcomings. Of course there is the Sigma 20 1.8 which is a topic for another day. The best solution in my opinion if is the Canon 20mm 1.8 EF USM. Excellent build quality (superior to Sigma EX) as well as excellent flare control. This is a very sharp lens which is great for landscapes as well as inside group pictures. The only negative is that you have to purchase the lens hood separately from Canon. That adds another 40-50 dollars to the price.