iTunes is the only software using which you can transfer all your mp3 song and video collection to your iPhone. Though you can also transfer songs without itunes but it doesn’t support storing of files like .doc, .ppt, .pdf etc on your iPhone.
DigiDna has come up with excellent free software called DiskAid which will allow you to transfer files with any extension (.doc, .ppt,.pdf,.xls etc) on to your iPhone and iPod Touch. The transfer of files is via USB between your iPhone and your Computer.
DiskAid is compatible with Windows and Mac OSX and it’ll automatically detect your device, be it iPhone 1st generation or iPhone 3G with support of firmware 1.1.1 through latest firmware 2.2 . The interface looks similar to Windows Explorer and you can directly drag and drop to store files on to your device.
And interestingly, DiskAid is available as a free download and NO Jailbreak or any hack is required to convert your iPhone or iPod Touch to USB external Disk. One you plugin your device, it’ll be automatically detected on your Windows and Mac (Linux is not supported)
Also, if you want to view .pdf, .ppt, .xls, .doc etc files on your iPhone, you can use FileAid which is another tool from DigiDNA. Though unlike DisAid it is not free, but it is just for $7 and you can directly download it from iTunes App Store.