You guys have all given just awesome tips. Samanax, I like what you said! I do want to get as much as I can out of my XSi! I know and feel it will do exactly what I want it to do when I learn all that I need to learn and know. I am to a point now where my XSi stays on the 'M' setting now. I will still use TV and AV for different things, but now I just mostly keep it on 'M' which is really causing me to full with the Aperture and the Shutter speeds also while selecting the proper ISO to go with it. OH I am loving it!!
Overread, I am going to look at that Sigma lens you mentioned. I'm not at all married to just using Canon lenses and supplies. I wouldn't mind jumping into something cheaper with the same exact quality.
-Christopher