You won't get much wider than the stock lens without spending decent moolah.
A 10-20mm Sigma lens is the lowest priced option or a Tokina 11-16mm or 11-20mm, but they are really for landscape work, and are only slightly different at the top end of your stock lens.
Beyond that, you would be looking at an 18-200mm maybe, to give more reach, but still that would have the widest at 18mm.
A 10-20mm Sigma lens is the lowest priced option or a Tokina 11-16mm or 11-20mm, but they are really for landscape work, and are only slightly different at the top end of your stock lens.
Beyond that, you would be looking at an 18-200mm maybe, to give more reach, but still that would have the widest at 18mm.