Based on the Marvel Previews #91, March for May 2011, I'd say you need to pre-order the following books in order to keep up with Spider-Man.
Core Titles
Amazing Spider-Man #660
Amazing Spider-Man #661
Amazing Spider-Man #661, X-Men Evolutions variant
Amazing Spider-Man #662
Astonishing Spider-Man & Wolverine #6
Fear Itself: Spider-Man #1
Spider-Man, Marvel Adventures #14
Ultimate Spider-Man #158
Ultimate Spider-Man #158, Steve McNiven variant
Guest Apps
Avengers Academy Giant-Size #1
Deadpool Annual #1
Heroes For Hire #5
Heroes For Hire #6
Heroes For Hire #6, variant cover
Moon Knight #1
Moon Knight #1, variant by Bryan Hitch
Moon Knight #1, variant by Humberto Ramos
Moon Knight #1, variant by TBA
New Avengers #12
New Avengers #12, X-Men Evolutions variant
Silver Surfer #4
Spin-Offs
Venom #3
Venom #3, X-Men Evolutions variant
Reprints
Amazing Spider-Man By David Michelinie & Todd McFarlane Omnibus HC
Amazing Spider-Man By David Michelinie & Todd McFarlane Omnibus HC, variant
Marvel Adventures Thor / Spider-Man Digest TPB
Spider-Man: Hobgoblin Lives TPB
Spider-Man: Matters Of Life And Death Premiere HC
Spider-Man: The Extremist TPB
Spider-Man: With Great Power Comes Great Responsibility #2
Spidey Sunday Spectacular #1
Ultimate Comics Doomsday HC
Ultimate Comics Spider-Man Vol. 2: Chameleons TPB