I`m going to audition for some of the orchestras at my uni this year, and I wondered if anybody could recommend some good audition unaccompanied pieces that are about Grade 7ish standard.
Thank you

Abi,
Sorry you had to wait so long for an answer. First, your professor might help you with some tips. The best piece is prepared highlighting your strengths; maybe one that you have already played for a competition or audition.
The Mozart Concerto is a grade 7 composition. Played well, it would work, but listen to it with orchestral accomp, not the piano, for a change. Your audition might only be 10 minutes or so, so pick a portion timed to fit. Know all of your major and minor scales and arpeggios, and chromatic to G. Practice sight reading like there is no tomorrow. If you have no piece prepared, try one from a method book, such as the Rose 32 etudes/40 studies. I believe it is around a level 7. If you have been in orchestra before, you know the pieces. Beethoven 1 thru 9, Shubert, Schumann #1, Shostakovich, Gershwin Rhapsody in Blue, Mendelssohn MidSummer Night`s Dream, Tchakovsky, Stravinsky (Firebird) and Sibelius #1, just to name a few.