My first uniform fetish would be military. My earliest memory of having a "sexual feeling" was at a War movie when I was around 8.
And then there was CHiPs. Any one remember the episode where the ladies went to a male exotic dancer club and one of the strippers looked like Poncherello? Often when I would drive by an accident on the freeway, you'll find me rubber necking, but not to look at the accident. I'm usually checking out the cops.
My vote goes to cowboys though. Right now there just something about those hats, jeans, boots, and gloves that intrigues me.