iNoRotate is a new application in Cydia, which disables the auto-rotate within applications on iPhone and iPod Touch.
Access iNoRotate application through Settings.app and either enable or disable applications.
Example: You’re laying down sideways and writing an email or SMS. The screens auto-rotates to landscape mode and you prefer portrait. Turning on iNoRotate and enable the application, disables auto-rotation for landscape mode.
iNoRotate is available in Cydia, from BigBoss repo, for FREE