As mentioed below, I like the Tamron 28-75 2.8 Di lens, cheap and sharp. Many people using it to replace the Canon 24-70 cause of close quality and the obvious price difference.
HOWEVER,,,, if focal length is an issue, I would wait to see some reports on the new Canon 24-105 IS. Should be pretty sweet, but I honestly havn't played with one yet.
Shot with the tamron 28-75 2.8 Di on a Fuji S2
JasonNJ
GPCB