Ok, I'll just jump in here, I'm new to this forum, been reading it for a while trying to get information on a lens too. I'm also just a hobby photographer.
Anyway, I settled on the Canon EF 70-300mm f/4-5.6 IS USM Lens after much reading and deliberating. I ordered it from SonicCameras for the great price of $309. Two days later they called for confirmation and tryed to push a similiar sigma lens priced at $449, citing problems with the compatibility of the Rebel XS and the Canon lens. I would not be swayed so a week later they sent me a notice that it was out of stock for at least eight weeks.
Next I ordered it from SLRGenius.com for $369. The confirmation call today informed me that it was a manual focus lens not for digital cameras. Again I was offered the similiar sigma for $599 or the canon 70-300 for digital cameras for $669. LOL
So my point is beware of the bait and switch.
I haven't re-ordered it yet, maybe tomorrow I will start browsing the web again for a more trustworthy vendor.