There are far too many possibilities to just arbitrarily throw them out, IMHO, without any clue about what form or what composer you have already listened to and enjoy.
If you have no clue whatsoever, Reference Recording has put out 5 compilation discs which have many short popular pieces by different composers what have been positively received by audiences for many years (thats why they are popular - DUH!). And the audio is great, thats what Reference Records are known most for, but these are pretty good performances as well.
While you're on RR site look up Rachmaninov's Symphonic Dances - Now thats a real demo disc as well as exciting, enjoyable, and assessible.
Also there have been numerous inquiries about classical music in the past. You might look up the threads I participated in several times for the benefit of persons new to classical seeking recommendations. You can note who some of the other participants who appeared in the threads and then look up their threads for other nuggets. Some guy called Texasdave(?) had a lot of good audio/performance recommendations as well as some others who regularily contribute to music inquiries.
Have fun. It sure has been for me (classical music that is).
