This fall, I am going to be a freshman at a medium sized university. I am going to be a music major (most likely concentrate on being a vocalist). I was wondering how the audtions are set up. Do I have to sight read a piece by ear? Have an accompianist? Or prepare my own material? Even though I was in choir for my high school years, voice lessons were never avaliable to me. So, I can't sight read vocal music completely.
First of all, i don't think you can sight read a piece by ear! Usually you sight read with your eyes, my dear 
But seriously, i think usually they will ask you to prepare a couple of pieces to sing for them, maybe from a list of songs they provide or maybe something of your own choosing. It's important to pick something that suits your voice and you're comfortable with.
I'm pretty sure they will provide you with an accompanist.
At my auditions i did have to do sight reading, but it wasn't anything awfully difficult.
Also they tested my aural skills, playing something on the piano which i repeated with my voice.
Hope this helps, and best of luck with your auditions!