I've got two: Bill Nye, and Brian Cox.
Bill, because I've had a crush on him since I was about 6 years old. He went from being my favorite kids show host to being on my favorite TV channel, the Science Channel. He's also just awesome.
As for Brian.... well, he's cute, a physicist (always an instant win in my book), and come on! That accent? Mop me off the floor why don't you!
Who are your geeky crushes?
Edit: this whole discussion is awesome. I guess I'm surprised that there are such a variety of crushes, but at the same time I'm not surprised.:)