I have a lot of music and video on my iPhone which I had to delete from my laptop to save space. Is there a way to backup EVERYTHING that is on my iPhone to an external hard drive and also restore from it?
The iTunes back up saves everything, but sometimes you are forced to restore to factory settings.
In that case,
Your apps are stored in iTunes
Contacts can be backed up with Google/Gmail, Yahoo or Mobile Me
Notes can be emailed to yourself (copy and paste back in)
SMS can't be directly backed up unless you're jailbroken