Here's a second vote for the Sigma 15-30mm EX DG. It is fantastic. I have 3 prints from this lens hanging in my home - two 11x14 and one 16x20. I find that I use this lens at the extremes, either 15mm because I am going as wide as possible, or 30 because I want to switch perspective to a "normal" wide. So long as there is enough light, I don't give up much compared to my primes, so I don't hesitate to leave the lens on the camera and shoot this way.
As for standing still.... I don't know how you could possibly stand still with a lens this wide. I move all over the place and contort myself into all kinds of positions, because positioning subjects, forground, background, and their relationships, are so critical to successful wide angle photos.