The Simga 50-150mm f/2.8 came into my mind when I bought my Tamron 17-50 f/2.8 VS (awesome for its price). I was close to getting it, till I found out it's for crop sensor bodies only. I guess getting the 70-200's will save me time in the long run.
Sigma is supposedly coming out with the stabilized version of the 50-150 f/2.8 zoom. I rented the mkii version of the unstabilized 50-150 f/2.8. Very nice lens, very good build quality. This lens is crop sensor only, but in exchange for that concession, you get a small package compared to the 70-200 f/2.8 lenses for full frame. The lens I rented was very nice and well constructed. I am not a pixel peeper or test chart shooter, but from what I could tell it had very good image quality. That lens is no longer available, but Sigma is releasing the long awaited update with image stabilization. If it has good image quality, I am definitely jumping all over it, as i shoot crop.