Well, if you want an example of a program, here's one I'm working on. It might be a little too "romantic," but it definately covers all style periods if you count Schubert as Classical! I would say to substitute something in the Schubert's place that is more "Classical," but the Schubert is the best piece! It's long, pretty, relatively easy (you just need to work REALLY hard on having the last movement clean cause it's pretty fast, though I'm not playing it at tempo for my exam). It's also not over played by any means. My program runs about 43 minutes.
Bach Prelude and Fugue in f sharp minor, book two. (Nice romantic prelude and moderately slow fugue which is a nice warm up).
Schubert Sonata in A Major, D 664
Brahms waltzes, 3, 4, 9, 11, 12, 13 from op. 39 (You could pick any number from that opus). I chose alternating fast and slow ones, starting with a slow one to give me a break from the sonata I just finished).
Rachmaninoff Prelude op. 23, no. 5 (not very original, but I HAD to play it, haha).
Chopin etude op. 10, no. 3 (well known, but a nice lyrical contrast after the Rach)
Bartok Roumanian Dance op. 8a, no. 1 (A MUST! Very very not overplayed, and a wonderful spunky contrast to the whole program. I love it.)
If you want recordings or videos of any/all of these pm me, but you can probably find most of them for free at Classicalarchives.com
It pretty much covers Baroque, a major sonata, Romantic, Early and Late 20th century. I only need to cover those. I don't know if you need impressionistic and whatnot as well. I would recommend some Debussy in that case.