I know this is an old post but thought I'd add in my two cents.
For any uni audition you should play some unaccompanied piece. Most unis ask for Bach. For me, I did the Sonata in G minor, unaccompanied. They usually ask for two contrasting movements (slow and fast). You should also have a good concerto under your belt. I switch between the Shostakovich Concerto in A minor and the Bruch Concerto in G minor. Most unis only ask for the first (or major) movement. You should also have a contrasting piece, usually written after 1800. I've done the Faure Sonata in A. Again, usually you will only be asked to play the first movement.
Hope that is of help to someone!