Hmmm... REALLY hard for me to narrow it down. In the past I've tended to overplay pieces when i first get infatuated with them, and then I tend to lose interest. I really try not to do that now, and I make an effort to get back to old favorites. But if I had to narrow it down:....
1) Brahms- Symphony #4. I've loved it since I first heard it in an introductory music appreciation class (back in 1970!!!) Overall, it's rather dark and dramatic, but NOT TRAGIC. By turns, it's brooding/mysterious, almost violent, idyllic, boisterously playful, and finally dark again. And I can just lose myself in the orchestration.
2) Randall Thompson- Symphony #2. This is more modern, written in the mid-1900s(?) Overall, it's a lot more energetic and exciting than Brahms'. Its second movement/section is slow- BEAUTIFUL melody, harmony, and orchestration. The ending is almost cinematic... you might be thinking, "Aww, I'm kinda sad it's over, but... WOW! WHAT AN ENDING!!"
3) Grrr. Do I have to pick just one other?... Maybe "Trail Of Broken Hearts", by k.d. lang... or "Kashmir", by Led Zeppelin... or "So Very Hard To Go", by Tower Of Power.
Phooey. I'll just go with the last 3. This thread did ask for "songs", and the first two don't really qualify, although Brahms (and Thompson too, I think) did write songs... or, at least, took text written by someone else and set it to music.