I am looking for a 'walkaround' lens under 200 bucks. I have a Canon Rebel XT, a 18-55 stock, and a Sigma 70-200 2.8 (awesome). Basically, I need something with a bit better range than my 18-55. Looking at the Canon 28-105, and the Sigma 28-70 2.8-4. The 2.8-4 sounds appealing since I take auto dirt track race photography at night. Any ideas? I know someone who's selling the Canon 28-105 used (like new) for 130.