I was actually screwing around with modeling a cactus, but XSI's normal map generator makes me want to stick something sharp into my brain
I even tried some 3rd Party tools, like NVIDIA's latest tool. It crashed whenever I tried to load my models.
Oh well, I'd probably get violent when I got to texture mapping, anyway.
My (unfinished) high-res model:
The low-res one is basically the same but w/o the ridges (and many less polys, of course)