Thank you all for your advice. I think it's going to be either EFS 17-55mm f2.8 IS USM or EF 24-70mm f2.8 L USM as soon as I get the $ together (not yet sure which one to complement my 18-85mm). I was tempted to go for a couple of primes, but fear I will be too limited unless I have a full set and that frequent changes will give me too much dust trouble.