17-50 is completely fine for a standard zoom lens on a crop sensor camera, and goes wide enough for most people.
It's also far more useful in every-day shit than anything wider than that.
However, if you're really looking at getting into Landscape photography or something, and you want serious wide-angle options, then something like the Tokina 11-16 f2.8 is far and away seen as the best option for this due to it's quality and speed.
Another option however, that will give you short-standard to wide angle would be the Tokina 12-24 f4. It's like 150$ cheaper than the 11-16 f2.8, and it has a longer zoom range, but again, it's f4, so quite a bit slower and made more as a landscape photography lens than a sports/indoor/low-light photo lens. Offers focal length equivalents from like 20mm-38mm, which is solid, and would perfectly compliment a zoom with 24 or 28mm being the wide end.
