In Canon you have the 24 f2.8, 28 f1.8, 35 f2.0 or the 35 f1.4 L. Both the 35's have good reps and I'm looking into a 35 f2 for myself in the near future. It really depends on how wide you want and how much you want to pay. All the Canon lenses are EF mount and need to be multiplied by 1.6 for the correct field of view for your 550D.
For Sigma you have the 24 f1.8, 28 f1.8 which are DG mount (same as EF mount) and the 30 f1.4 which is a DC mount lens (same as EF-S). The 30 1.4 has also got a very good rep but not suitable for a full frame body unfortunately, otherwise I would of got one of these.
I have no knowledge of any Tamron primes in this range or even if there is any and IIRC the Tokina primes are manual focus only, but I'm sure some of the wonderfully knowledgeable people on here will be able to answer that for you soon.