Also http://www.adorama.com is a good reasonable priced place to shop...

As for the Sigma lenses.. they are as good as the Canon glass IMHO (when talkign the entry level stuff).. The lower the F# the better the pics will be.. I have the Sigma 70-300mm zoom and the 28-80mm and both lenses are decent.. Now remember to convert to digital the mm will be x 1.6 http://ocsurfer.deviantart.com to check out some of my other shots as well as my gallery here has some with the 300D and the Sigma lenses.. The 70-300mm could be sharper at the lower f# but shooting at f8-f11 on a tripod at full zoom works out nicely A great middle priced starter lens would be the Canon EF 70-200mm f/4 ($500-$600)http://www.usa.canon.com/html/eflens..._70-200_4.html
http://www.usa.canon.com/html/eflens.../ef_50_18.html This is also a great lens that can be had for <$90 not much for tele or anything but a great all around lens.

The fixxed aperature lenses tend to be much better IMHO... Remember you can also get a tlel converter 1.4x-2x if need more zoom.