What exactly is included when I backup my iPhone 4 using iTunes? I have read this question Does an iTunes iOS device backup include everything on the device? but it doesn't seem to be explicit/succinct enough and I can't find a clear list of what exactly is and isn't backed up anywhere that I would trust.

Specifically I am asking which of these things are backed up ( and if there are any others which I am leaving out )


Settings inc email settings and and wifi passwords
Applications and their settings
Photos
Videos
Songs
Notes
Reminders
Calendar
Voice Memos
Contacts
SMS's
Firmware ( which I gather is not backed up )


I have a feeling that various parts of the backup are stored in various locations so maybe that might be explained, and also I read somewhere that the backup only includes the media items if a sync has been performed so could this be explained ... ie do I have to also do a sync to ensure a full backup.

I have an iphone4 and I am backing up to my computer as opposed to iCloud.
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.