iPhone Folders is an excellent application for iPhone that integrates into Windows Explorer and allows access to all files and folders of the iPhone , just like an USB stick.
Using this extension you can browse your phone filesystem, copy files to and from it, open files directly from iPhone, create shortcuts to folders on iPhone. In thumbnail mode program will display previews of png and jpg files on phone, application icons for installed applications (.app folders).
Compatible with x86 editions of Windows XP, Vista, 7 and x64 editions of Windows XP, Vista (unlike Vista, Windows 7 x64 can’t be forced to execute Windows Explorer in 32bit mode, so no Win7 x64 support for now). Requires iTunes 8 or 9 for normal operation. Supports jailbroken and non-jailbroken phones (in the later case filesystem access is limited to Media folder).
You can watch a demo video and download iPhone Folders here.