David Lau , Mar 24, 2005; 03:03 a.m.
There is a current Tamron 28-105/f2.8 zoom, though the image quality is average. I also own the previous generation Tamron 35-105/f2.8, which can produce much better quality images. You may be able to find it used.
For portrait work I always use prime as I do not find the need to change focal length frequently. I can always step forward or back to get the framing I wish. My favourite lens is 85/f1.8. f2.8 is too slow for the shallow DOF I am looking for in portraiture.