Echoes in my opinion is the definitive Floyd song.
Their best albums IMO along with my favorite track:
1.Dark Side of the Moon (Time)
2.Piper at the Gates of Dawn (Astronomy Domine)
3.Wish You Were Here (Shine On You Crazy Diamond, Parts I-V
4.Animals (Dogs)
5.Meddle (Echoes)
6.Atom Heart Mother. (Fat Old Sun
7.The Wall (Nobody Home)
9.Division Bell (Marooned)
8.Obscured By Clouds (Burning Bridges)