Messian has a lot of great stuff, quartet for the end of time is pretty well liked.
I really like Vaughan Williams, I'd suggest The Lark Ascending, it's a violin concerto, I also really like his greensleeves.
Are you looking for purely tonal things? I mean, that's pretty much what has been suggested so far, but how much atonality can you handle/enjoy?
Saint-Saens Symphony no 3, The Organ Symphony would be good to pick up
What about picking up some Charles Ives stuff? he's not played all that much. I really enjoy his quartets.
I second Shostakovich, anything by him, but his 5th symphony is probably most known (don't let that turn you away from it) I would also get his Cello concerto's, there are two.
Weburn is also amazing, I forget the pieces name, 7 sketches maybe...I can't remember off the top of my head.
Schoenberg wrote some interesting stuff too.
Why not just go to your local library, pick up some random CD's, don't even look at them, listen to them, read the notes that come with the CD and see which of those you like and which you don't. the interesting thing about classical music is the more you know, the more stuff you like. So, don't write off a piece write away, or at least, give it another chance a few years down the line.
Where do you live? The reason I ask is that you could also go and see your local orchestra, you might also live near a conservatory or really great music school if there isn't a great orchestra near you. Seeing a piece performed is just a different feeling than listening, and I feel like the more performances you see, the better classical music gets (at least for me).