Know these names:
Rachmaninoff, Orff, Bizet, Mozart, Prokofiev, Stravinsky, Vivaldi, Tchaikovsky, Telemann, Bach, Dvorák, Rimsky-Korsakov, Offenbach, Liszt, Chopin, Wagner, ... eh, just tune into your city's classical station or listen to one on Internet Radio before the RIAA kills it.
Good current classical performers are Gil Shaham, the Orpheus Ensemble, Eroica Trio, among many others... and likely your own city's orchestra. Check out your local performers, there's probably always interesting stuff going on. Local colleges will also often have free or cheap concerts.
There's also modern stuff going around. John Williams has a bit of stuff besides Star Wars, and there are groups like Bond that pep-up existing classical stuff with their own style or others who mix-n-match with their original music. (Of course, some people like looking at Bond more than listening to them, which I can understand, since I think their sound is silly.)
Also, free Creative Commons-licensed classical music downloads:
http://www.musikethos.org/wiki/me.php/Main/HomePage/