What kind of sports are you shooting?
The Tamron 28-75 F2.8 would probably be good for indoor/gymnasium sports (~$400 new). I don't have one, but I am looking at getting one for next years basketball season. Another lens I'm looking at for basketball is the Pentax 50-135 F2.8 (~$1,100 new).
For hockey, I use a Sigma 70-200 F2.8, but it would be around $1,000 new. The least expensive 70-200 F2.8 would be the Tamron, which would be around $800 new.
This year I've been using the Sigma 70-200 for softball also, but I used the Pentax 55-300 last year and it works well during sunny days. I've been contemplating getting the Pentax 60-250 F4.0 for softball, but it's not cheap at ~$1,500+ new.
Last edited by JeremyP; 06-14-2011 at 10:22 AM.