X4?

If you click here, you'll find out that there will be an X-men 4. Some other Marvel films or projects in development or post-production include:

Marvel Character Feature Film Line-Up For 2007
Ghost Rider, Sony - In post-production, February 16, 2007 release
Spider-Man 3, Sony - In production, May 4, 2007 release
Fantastic Four 2, Fox - In early pre-production, July 4, 2007 release

Film Projects Being Developed by Marvel (Partial List)
The first film is anticipated for release in 2008.
Ant-Man, Marvel - Writer and director engaged (co-writer/director Edgar Wright, Shaun of the Dead)
Captain America, Marvel - Writer engaged (David Self)
Hulk 2, Marvel - Writer engaged (Zak Penn of X2, X-Men 3)
Iron Man, Marvel - Writer and director engaged (Arthur Marcum and Matt Holloway screenwriters. Jon Favreau is the director.)
Nick Fury, Marvel - Writer engaged
Thor, Marvel - Writer engaged (Mark Protosevich, Poseidon)

The Avengers, Black Panther, Cloak & Dagger, Doctor Strange, Hawkeye,
Power Pack and Shang-Chi are also projects to be developed by Marvel.

Marvel Character Licensed Film Development Pipeline (Partial List)
Wolverine, Fox - TBD
The Punisher 2, Lionsgate - TBD
Magneto, Fox - TBD
Namor, Universal - TBD
Luke Cage, Sony - TBD

Marvel Character Animated TV Projects in Development
Fantastic Four, Moonscoop SAS (France) - 26, 30 minute episodes airing in 2006; U.S. distribution expected on Cartoon Network
Wolverine, First Serve Toonz (India) - 26, 30 minute episodes in development
Iron Man, Method Films (France) - 26, 30 minute episodes in development

Marvel Character Animated Direct-to-Video Projects in Development
Partnership with Lionsgate to develop, produce and distribute original animated DVD features. Titles include: Ultimate Avengers (released February 21, 2006), Ultimate Avengers 2 (scheduled for Q3 2006), Iron Man and Doctor Strange.

Marvel Character Live Action TV Projects (Partial List)
Blade, in production and premiering on Spike TV in June 2006; Alter Ego and Skrull Kill Krew in development