For me there are two kind of melancholic tracks. The pure meloncholic ones like Midian, Coming Home, Pathfinder like Paradox posted, Rain, Axis V.99 and the nostalgic ones.
The nostalgic don't make me really sad, more put a bittersweet smile on my face. Hard to explain it.
Some examples of nostalgic tracks are Oforia-Voice Of Delusion & The Morning Song, California Sunshine-The Deeper The Bluer, Doof-Sunshrine, Tandu-Rodeo etc.