Pink Floyd were an English rock band who in the 1960s earned recognition for their psychedelic and space rock music, and in the 1970s, as they evolved, for their progressive rock music. Pink Floyd's work is marked by philosophical lyrics, sonic experimentation, innovative album cover art, and elaborate live shows.

One of rock music's most critically acclaimed and commercially successful acts, the group has sold over 200 million albums worldwide including 74.5 million certified units in the United States. Pink Floyd influenced progressive rock artists of the 1970s including Genesis and Yes, as well as contemporary artists such as Nine Inch Nails and Dream Theater.

YouTube - The 40 Best Pink Floyd Songs

My personal list with my opinion on the 40 best Pink Floyd songs. You should know that there is a lot of other songs that I really like, but that didn't make it to the list.
Several weeks of analyzing and reviewing has made this list. Hope you enjoy!

COMPLETE LIST
Pink Floyd (Top 40 - Best Songs)

The songs are taken from 10 different studioalbums (every studioalbum, except for "Ummagumma"), 1 soundtrackalbum and three singles.

1. Echoes (1971, "Meddle")
2. Comfortably Numb (1979, "The Wall")
3. Shine On You Crazy Diamond - Part VI - IX (1975, "Wish You Were Here")
4. Time (1973, "The Dark Side of the Moon")
5. Wish You Were Here (1975, "Wish You Were Here")
6. Learning to Fly (1987, "A Momentary Lapse of Reason")
7. The Great Gig in the Sky (1974, "The Dark Side of the Moon")
8. Money (1973, "The Dark Side of the Moon")
9. Interstellar Overdrive (1967, "The Piper at the Gates of Dawn")
10. Breathe (1973, "The Dark Side of the Moon")
11. Set the Controls for the Heart of the Sun (1968, "A Saucerful of Secrets")
12. One of These Days (1971, "Meddle")
13. Welcome to the Machine (1975, "Wish You Were Here")
14. Hey You (1979, "The Wall")
15. Us and Them (1973, "The Dark Side of the Moon")
16. Brain Damage/Eclipse (1973, "The Dark Side of the Moon")
17. High Hopes (1994, "The Division Bell")
18. See Emily Play (1967, Single)
19. Dogs (1977, "Animals")
20. Another Brick in the Wall Pt. 2 (1979, "The Wall")21. Pigs (Three Different Ones) (1977, "Animals")
22. A Great Day for Freedom (1994, "The Division Bell")
23. Run Like Hell (1979, "The Wall")
24. Keep Talking (1994, "The Division Bell")
25. Arnold Layne (1967, Single)
26. Careful With that Axe, Eugene (1968, Single)
27. Astronomy Domine (1967, "The Piper at the Gates of Dawn")
28. Sheep (1977, "Animals")
29. Mother (1979, "The Wall")
30. Have a Cigar (1975, "Wish You Were Here")
31. A Saucerful of Secrets (1968, "A Saucerful of Secrets")
32. Fat Old Sun (1970, "Atom Heart Mother")
33. Young Lust (1979, "The Wall")
34. Let There Be More Light (1968, "A Saucerful of Secrets)
35. The Nile Song (1969, "Soundtrack From the Film "More"")
36. Is There Anybody Out There? (1979, "The Wall")
37. Bike (1967, "The Piper at the Gates of Dawn)
38. Coming Back to Life (1994, "The Division Bell")
39. The Trial (1979, "The Wall")
40. The Fletcher Memorial Home (1983, "The Final Cut")