How wide you want it, OP? Because the widest non-fisheye canon lens is the 14mm f/2.8 L...
INSANELY expensive. Samyang makes a very cheap all manual 14mm, it outperforms the canon one, but you get a very nasty distortion (almost fisheye) which is a bit difficult to get rid of. At least it's cheap, wide and well built.
If you just want a reasonably wide but not TOO wide lens, the 20mm f/2.8 USM should be good. But I think the 17-40 should easily outperform it at the same focal lenght.
>>1253835>was thinking of replacing it with the Sigma 50mm 1.4, heard great things.You heard right, it's a great lens, especially on crop. And it's built like a tank.