I'm looking for new lenses to add to my collection. I recently found an EF 35-80mm medium telephoto lens labelled as Rebel and 50/10/7D compatible, and I'm curious if it will be compatible with my t1i rebel?
You mean this lens?
If so, yes, it'll work fine with with any Canon EOS camera regardless of model.
Note that the range on this lens will go from a focal length which appears fairly "normal" to a focal length that appears moderatley (but not greatly) zoomed in. It will not provide any wide-angle range on your camera (it would if it were on a "full frame" camera body such as a 6D, 5D series, or some of the 1D series bodies as well as one of the old EOS film bodies.)