It sounds like you are more than ready to enter a college program now. As for sight reading, you should generally read pieces a couple levels below the repertoire you are playing. I would suggest the following:
Baroque : Handel suites, anything by Bach, Rameau, Couperin, Scarlatti
Classical : sonatas by Mozart, Haydn, Beethoven, Clementi, etc.
Romantic : Liszt pieces from the Years of Pilgrimage, Chopin nocturnes, waltzes, preludes, mazurkas, Schumann Scenes from Childhood, etc.
20th century : Prokofiev Fugitive Visions, Sarcasms, etc., Debussy preludes, Scriabin preludes and other shorter works
Most of the above can be found in cheap dover editions, which would be perfect for sight reading practice. If you were learning any of these pieces, you may want to find a better edition, but dover will be fine for just sight reading.
Milton