Wow this is a hard one!
Ermmm...
Best ever is probably Pink Floyd at Wembley Stadium in '87, but others that stand out are..
Motorhead in '79,
Iron Maiden in '80
Ian Jury & The Blockheads in '80
AC/DC in '81
Thin Lizzy in '83
Rainbow in '84
Van Halen in '84
Metallica in '90
More recently..
Razorlight, PJ Harvey, The Subways, The Music, Foo Fighters