I too have an XTi. I just bought the body for it in January and carried over the lenses that I had from my Canon EOS Rebel Ti. I think one was a 28-75mm lens and the other a 75-300mm lens.
Recently picked up an Optech Pro loop camera strap, a knock off Gary Fong Lightsphere light diffuser for my 420EX flash and a wireless remote shutter release. Also picked up two Mennon white balance lens caps (that I'm not really thrilled with) and an el cheapo backup battery that so far seems to be working pretty well.
I've also got a Tiffen circular polarizer and a neutral density filter that I only rarely pull out. But need to pick up a UV filter and might want to pick up a graduated ND filter for situations that call for it.
Looking to buy another 2GB CF card for backup, a mini tripod (or beanbag), and a new Tamrac bag or backpack to fit it all in now that I've outgrown my old Canon bag.