Based on the Marvel Previews #79, March for May 2010, I'd say you need to pre-order the following books in order to keep up with Spider-Man.
Core Titles
Amazing Spider-Man #631
Amazing Spider-Man #631, heroic age variant
Amazing Spider-Man #632
Amazing Spider-Man #632, heroic age variant
Amazing Spider-Man #633
Amazing Spider-Man #633, heroic age variant
Amazing Spider-Man Annual #37
Astonishing Spider-Man / Wolverine #1
Astonishing Spider-Man / Wolverine #1, foilogram variant
Peter Parker #3
Spectacular Spider-Girl #1
Spider-Man, Marvel Adventures #2
Spider-Man: Fever #2
The Many Loves Of The Amazing Spider-Man #1
Ultimate Spider-Man #10
Web Of Spider-Man #8
Web Of Spider-Man #8, heroic age variant
Guest Apps
Age Of Heroes #1
Age Of Heroes, heroic age variant #1
Amazing Spider-Man Presents: American Son #1
Amazing Spider-Man Presents: American Son #1, heroic age variant
Avengers, heroic age variant cover Greg Land #1
Avengers, regular cover #1
Avengers, variant cover John Romita Jr. #1
Avengers, variant cover Marko Djurdjevic #1
Hulk #22
Hulk #22, variant
Marvel 1602 #1, Marvel's Greatest Comics
Marvel Zombies #1, Marvel's Greatest Comics
Origins Of Marvel Comics #1
Reprints
Heroic Age Magazine, 50/50 covers by Jim Cheung #1
Marvel 1602: Spider-Man Premiere HC
Marvel Masterworks: The Amazing Spider-Man Vol. 4 TPB
Marvel Masterworks: The Amazing Spider-Man Vol. 4 TPB, variant edition
Spider-Man Magazine #11
Spider-Man: Noir - Eyes Without A Face Premiere HC
Spider-Man: Red-Headed Stranger TPB
Spider-Man: The Complete Clone Saga Epic Book 2 TPB
Spider-Man: The Gauntlet Vol. 3 - Vulture & Morbius Premiere HC
Spider-Man: The Real Clone Saga HC