The short answer is: "None" See the answer for the question: Are canon t70 and canon eos rebel xsi lense compatible? The Canon AE1 takes FD mount lenses. All Canon digital cameras take EF lenses. They are not compatible.
Unfortuntely, No you can not use the AE1 Program lenses with Canon EOS cameras. They use different types of lenses, thus the diameter, connections and mount are different.
The Canon AE1 lens will not fit a Canon digital. You can buy an adapter that will allow the lens to work in manual focus mode on the digital camera.
With just the standard lens? Maybe as much as $40 if it's in pristine shape. They can be had on eBay for $20.
The AE-1 lenses have Canon's FD breech-lock lens mount. They are not compatible with Canon's later EF lens mount. It may be possible to find an adapter, but performance would be lost, and the lens will not have the features of an EF lens. Best to save your money and get a dedicated lens, either Canon or Sigma.
No.
The Canon EOS Rebel, Rebel XT, and XTi are EF-S mount. They will accept EF-S and EF mount lenses.
Yes, you can. It has a Hot Shoe Mount.
No, the lens mount is completely different.
The Canon Eos lense mount, the "bayonet-style mount" is known for taking pictures through electrical contacts, in contrast to the conventional way of camera shots.
All Canon Rebel DSLR cameras uses EF lenses that fit the Canon EF Mount.
Yes, with a FD to EOS mount adapter.