You can look at my list below, Sigma EX is about all I own. I love them. The small difference some seem to notice isn't worth paying almost twice the amount for a Canon or Nikon lens. If you want image stabilization, then stick to the Canon or Nikon, but if you don't want that then Sigma is the way to go.
Check out my portfolio at
www.pbase.com/dbphotos or
www.sportsshooter.com/dbphotos all the sports images are shot with Sigma lenses.