Definitely have to agree with 'Wish You Were Here', but I also think that 'Welcome to the Machine' and 'Have A Cigar' are brillaint songs, also 'Orion' by Metallica is another awesome song.
Master Of Puppets & Enter Sandman are definately there, moving more to the heavy stuff, Hallowed Be Thy Name by Iron Maiden and a bit of classic rock, Cryin' by Aerosmith.
I've been thinking about this for a day now, and I think I've narrowed it down to my top five all time. In no order,
Strawberry Fields Forever - The Beatles
Blue in Green - Miles Davis
Predatory Wasp of the Palisades - Sufjan Stevens
Amie - Damien Rice
Lion's Mane - Iron & Wine
I'm clicking Submit now before I have a chance to change my mind.