Originally Posted by epearson
I wouldn't try and create some kind of ratio to determine or justify your lens choice. The best lenses tend to be the most expensive (think "L").
A very decent step up from the kit lens is a lens that performs well on smaller sensor cameras than full frame, so it would be a decent choice for your XT. The...
Canon EF 28-135mm f/3.5-5.6 IS USM
There is even a review about it here on this site. You can get then new around $399-$409 on discounters sites. Less if you shop for a refurb or a used one on ebay.
I took some stunning photos with that lens and a 30D back when I first started shooting a few years ago. Once you start creeping up into higher end products you truly start to appreciate good glass. A good sensor is key, but great glass is killer. If you can jump all the way to L's then definitely read the reviews here on this site.
Michael James