Hi Dutch and welcome,
Congratulations on your new dslr and lens!
There are literally scores of styles of tripods to choose from, in all different price ranges. Some of the better-known tripods are made by Bogen, Monfrotto, Gitzo, Sunpack, the list goes on. You can also get tripods under a camera manufacturer's name such as Canon and Nikon.
It's difficult to recommend a specific tripod because there are so many options. You will, however, need a well-constructed, well-balanced one to hold the XSi mounted with a 300mm lens. If you're photographing wildlife, you may want to consider a tripod with a pan head.
Before buying a tripod, no matter which brand, make sure you become familiar with the features and get a tripod which best meets your needs.
Tripod features: http://www.digicamhelp.com/accessories/tripods/tripod-features/ Make sure the tripod head suits your shooting style:http://www.digicamhelp.com/accessories/tripods/tripod-heads/
