What exactly is included when I backup my iPhone 4 using iTunes?
Apple has a great article enumerating what gets backed up for each level of iOS.


iTunes: About iOS backups 


Pay close attention to the section titled iTunes will back up the following information and note that by setting a passcode, Apple backs up more of your device's keychain. Also this article covers using iTunes and iCloud to back up since each has strengths and weaknesses in terms of backing up an iOS device.

In terms of the things you enumerate - all are backed up except the one you didn't want (the OS itself and firmware for the device).

I would encourage you to also sync contacts (and other data) so you have a second backup (or even the ability to make a third backup of the synced data) since losing contacts is an event that is very painful to recover.