What camera lens should I buy?

That depends entirely on what you want to photograph!

Assuming you have the 18-55mm lens then you would buy the 17-40 if you wanted an increase in image quality or the 24-105 if you wanted increased image quality and a longer reach.

What do you want the new lens for? I assume you already have the 18-55mm lens. If you find yourself backing up just to get more at 18mm, get something much lower than 18mm. 17mm isn't that much. If you are wanting to get much more closer even if you are already at 55mm, get a longer lens like a 300mm. If you continuously want to shoot longer after the sun sets, get a faster lens, one with the lowest f/number you can afford that is lower than f/3.5. If you seem to be engrossed at making very little things seem large, get a macro lens, one that can focus at the distance you want to work at. You buy a new lens to broaden your versatility and not to replace your old one.

Those are great lenses, but you would be paying a premium price for the ability to work with a full frame body that you don't have. You might get more value for the money looking at EF-S lenses for your APS-C body.