Nick, the Fortingall yew is an outstanding tree, well worth a visit if you ever get a chance.
A very understated attraction in the area. Very exciting too, as it is obviously still very much still alive and is more than likely still got a lot of life in it and will continue to outlive many generations of humans yet.
This is pretty much all that is left of it after its rather eventful history:
Also if I can just echo John's comments about the ancient tree hunt too, as a verifier on the project we really need you guys to assist by entering the details of the big trees around you that you know of. Just because its a popular tree, don't leave it to others to put it up, you may be surprised and find that no one has entered it and your name will go down next to it as it's "discoverer". Please get envolved! It might help secure the future of some seriously old trees!