What does iTunes back up
iTunes will back up this information:

Camera Roll (photos, screenshots, images saved, and videos taken)
For devices without a camera, Camera Roll is called Saved Photos.
Contacts* and Contact Favorites (You should regularly sync your contacts to a computer or cloud service, such as iCloud.)
Calendar accounts and subscribed calendars
Calendar events
Safari bookmarks, cookies, history, offline data, and currently open pages
Autofill for webpages
Offline web app cache/database
Notes
Mail accounts (mail messages aren't backed up)
Microsoft Exchange account configurations
Call history
Messages (iMessage and carrier SMS or MMS pictures and videos)
Voicemail token (This isn't the voicemail password, but it is used for validation when connecting. This is only restored to a phone with the same phone number on the SIM card)
Voice memos
Network settings (saved Wi-Fi hotspots, VPN settings, and network preferences)
Keychain (includes email account passwords, Wi-Fi passwords, and passwords you enter into websites and some apps)
If you encrypt the backup, you can transfer the keychain information to the new device. With an unencrypted backup, you can restore the keychain only to the same iOS device. If you're restoring to a new device with an unencrypted backup, you need to enter these passwords again.
App Store app data (except the app itself, its tmp, and Caches folder)
App settings, preferences, and data, including documents
In-app purchases
Game Center account
Wallpapers
Location service preferences for apps and websites you've allowed to use your location
Home screen arrangement
Installed profiles
When you restore a backup to a different device, installed configuration profiles aren't restored (such as accounts, restrictions, or anything that can be specified through an installed profile). Any accounts or settings that aren't associated with an installed profile will be restored.
Map bookmarks, recent searches, and the current location displayed in Maps
Nike + iPod saved workouts and settings
Paired Bluetooth devices (which you can only use if restored to the same phone that did the backup)
Keyboard shortcuts and saved suggestion corrections
Trusted hosts that have certificates that can't be verified
Web clips