Haha, wow, what a question. It was so long ago. I can't narrow it down to one, but it was either Brandy Scott or Christie McNicole. This was way back in the days when the two were still actively making movies, probably around the year 2000.
I was mesmerized by them, partly because before them I had never heard of transsexuals and was so intrigued by what I saw, and two...they were both gorgeous (these pictures don't do them justice...).
I wonder what they're doing nowadays. I've heard, through my years of surfing, that Brandy Scott is a real bitch.