[anxela]

I don't have a zoom lens in that range, but I do have a Sigma 50mm f/1.4. It's amazing. Really. The bokeh is so smooth. Actually, the man in the camera store recommended this over the Canon 50mm f/1.4, and I think it says something when they recommend the non-brand name. It's heavier than the Canon, but it justifies it with image quality. I've heard a lot of praise over Sigma lenses lately, and I would not hesitate to buy Sigma again.

I'm going to buy a new and wider lens soon, but I can't make up my mind about getting the Sigma 18-50 f/2.8 zoom or the Sigma 30mm f/1.4 prime that Aino mentions.

I haven't tried Tamron, but I've heard lots of good things about their lenses, too.

Just one little note - if you imagine yourself upgrading to a full frame body, you might want to look at the 24-70 or 28-75 instead of the 17-50/18-50, if you can do without the extra wide angle for now.