The same things that are backed up in a standard iTunes backup are backed up to iCloud.
App Data, App Homescreen Placement, Settings, Camera Roll, probably many more things that I'm forgetting.
The only two things not backed up by default are the music on the phone and the actual apps.
When you restore from the backup the phone will automatically redownload all apps you had at the time of last backup from the appstore.
You also have the option to disable the backup of individual data such as the camera roll if your backup was proving to be too big for your iCloud data allotment.
I believe the options are under Settings >> iCloud >> Storage and Backup.