Video backup solution in the Cloud
It's awkward to have iPhoto libraries on both internal and external disks. Aperture might be a better solution or you might want to just manage your videos outside of iPhoto instead.

Crashplan has some inexpensive unlimited backup plans available. It also can do additional backups to another local machine or locally attached hard disk.

My personal practice is to have a local backup and a remote backup using two different technologies so I use Time Machine locally to a Mac Mini that's my home server (although a Time Capsule or local hard disk would work just as well) and Crashplan for remote backups. Having a local backup is much more convenient so the remote is strictly for major disasters.