To those who think nothing of suggesting a £900 lens to someone with a budget of, at best, less than one third of that:
Those nice expensive lenses might be great and suit you (and your wallet) down to the ground, but please have a care for people who are on a tight fixed budget and clearly state that budget in their opening post. Is it not more constructive all round?
There is a lot more to choosing lenses than differences in image quality that can be hard to discern and matter nought to almost anyone who looks at someone's photos other than the person who has to justify the expenditure of that kind of money. The kind of cash that some of us would take many months to scrape together once the bills are paid and simply could not justify by any form of rational thought even if we could afford it.
To the OP: the Sigma 30mm is a cracking lens in every way, but I can understand that it might be a stretch. Sigma's 28mm f/1.8 is a bit cheaper and I reckon that you would be quite happy with it. The Canon 28mm f/1.8 USM is about the same price as the Sigma 30mm, so I can't really favour it. I have never used Canon's cheap 35mm f/2, so I have no opinion about that.
Whatever you pick, try to stick with f/2 or wider rather the f/2.8s, since that is obviously one of the biggest benefits of a prime.
(My comparisons based on UK prices, obviously. YMMV)