You probably don't need an extra battery but if you do, check out
www.sterlingtek.com, you can get two of them for around $20 plus shipping.
The camera itself won't come with a memory card, so you will need one. Many places will include one when you buy a camera, but that depends on where you buy and what 'kit' you get. There are plenty of places to get memory cards, Costco is usually pretty good (if you have a membership). I hear that Newegg.com is a pretty good site for that, but they don't deliver to Canada, so I don't know for sure.
The 28-135mm IS, is a decent lens for starting out. My one concern is that it won't be very wide on a camera like the XTi (or any of the digital rebel models or the 20D, 30D, 40D etc.)
I would recommend the EF-S 17-85mm IS, which is basically the same lens, but in a digital only EF-
S format. That's a personal choice though, but I do suggest you get into a camera store to try out those lenses on that body, just to be sure that you know what you are getting.
So besides a memory card, you shouldn't
need anything else to start out with. Plenty of optional stuff to think about though...Maybe a camera bag, tripod, circular polarizing filter.