Consider looking for a used 28mm f1.8. I think it works really well with aps-c sized sensors, giving a equivalent full frame view of ~45mm. I used almost exclusively this lens with my 600d.
+1. I've been using that lens with my 500D. Now, I'm still using it with my 6D and it seems to be sharper than ever. Together with the 50mm F1.8 II, I've got a fairly light combo. The fact that it focuses fast even in low-light is a plus especially indoors. There are lot of people selling theirs after they moved from APS-C to FF due to the kit lens they got when buying their FF. You can get a lot of deals for this lens. For me, I'll keep mine. It's very useful for me. It's sharpest when used @ F2.8 and above but F2.2 is sharp enough especially for portraits.