I would try to recommend the Tokina 11-16 2.8 (for crop body) like the 40D. Its sharp & fast. Great for wide angles in low light. You might want to try the Sigma 10mm 2.8 fisheye.Like the above mentioned, its sharp & great in low light shooting as well. If you like exaggerated distortion, this is your tool. You can "de-fish" it with PTLens.