Archiving / Backup of Design/Video work

We are a small design agency and are trying to improve our archive system. Currently we backup all projects (excluding video as it's too large), onto DVD, plus a duplicate DVD which we store off-site. It's a bit of an out-dated system so we are interested to find out if others have a better solution?

We also duplicate all work onto an external hard drive for ease of access, but it's more a question of how to handle an offsite copy of all archived work.

Also, has anyone used Time Machine - it looks interesting but a bit worried as to how fast it will fill up a TB if it's archiving every day?

Thanks for your suggestions! :)