Many people ask me about the Sigma 30mm f1.4 prime lens. I've owned it both in a Canon and a Nikon mount, and I can say both of mine were fantastic. Prime lenses aren't for everybody, but if you're a prime shooter or are just interested in adding more flexibility to your lens line-up, I'd highly recommend you try the Sigma 30mm f1.4.
At f1.4, you'll have to watch your distances and make sure what you want to be in focus will be, but it's a look you're not going to get from a slower lens. I'm talking about that creamy, out of focus background. You just can't get that at f8, or even at f2.8 for that matter.
There have been reports that some samples of this lens aren't sharp. While this may be the case, I can tell you that both of mine were extremely sharp. Bear in mind too, that you're just as likely to get a new Canon lens that isn't sharp (MORE likely with some Canon lenses), as you are with the Sigma 30mm f1.4, so don't let that stop you. Shop at a store that will let you try it out first, and you shouldn't have any problems. I can also tell you that customer service for Sigma is fantastic. I spoke with them at length about another Sigma lens I was considering buying 2nd hand, and they were very helpful.
Did I mention my Sigma 30mm's were sharp...
Sigma 30mm @ f1.4