Center Stripe Agave, Thorn-crested Agave (Agave lophantha)
This is not a photo of Agave triangularis, which looks like this:
Your leaves are wider and have a stripe in the middle. Your picture is a photo of Agave lophantha instead. http://davesgarden.com/pf/showimage/42657/
Would you like this image moved to the Agave lophantha page?