Based on the Marvel Previews #90, February for April 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 #658
Amazing Spider-Man #658, Thor Goes Hollywood variant
Amazing Spider-Man #659
Amazing Spider-Man Annual #38
Spectacular Spider-Man #1000
Spider-Man, Marvel Adventures #13
Ultimate Spider-Man #157
Ultimate Spider-Man #157, Ed McGuinnes variant
Guest Apps
Avengers #12
Avengers #12.1
Avengers: The Children's Crusade #5
Carnage #4
Fear Itself #1
Fear Itself #1, Blank variant
Fear Itself #1, Fantastic Four variant
Fear Itself #1, Steve McNiven variant
Fear Itself #1, Stuart Immonen variant
House Of M - Marvel's Greatest Comics #1
New Avengers #11
Ultimate Avengers Vs. New Ultimates #3
Ultimate Avengers Vs. New Ultimates #3, variant cover Frank Cho
X-Men #10
X-Men #10, Thor Goes Hollywood variant cover
X-Men #10, variant cover
Spin-Offs
Venom #2
Reprints
Acts Of Vengeance Crossover Omnibus HC, Alan Davis cover
Acts Of Vengeance Crossover Omnibus HC, Liefeld cover, direct market only
Astonishing Spider-Man & Wolverine: Another Fine Mess #1
Marvel Adventures Spider-Man: Sensational Digest TPB
Spider-Man: New York Stories TPB
Spider-Man: One Moment In Time TPB
Spider-Man: The Death Of Jean DeWolff Premiere HC
Spider-Man: The Death Of Jean DeWolff Premiere HC, variant edition
Spider-Man: With Great Power Comes Great Responsibility #1
Thunderbolts Classic Vol. 1 TPB
X-Men: First Class - Class Portaits TPB