What is a quick / easy way to backup your data?

External Hard Drives are awesome.

I'm a photographer-on-the-side, so I actually have a giant binder full of DVD's with archived shoots. Every couple of months my hard drive fills up, and I dump the whole thing off to DVD's -- if you're a Mac person, check out http://discoapp.com/

Mozy is a great program. It automatically backs up your data in the background, and gives you 2GB of storage free. Give it a try, I think you'll like it.

General/daily: External hard-drives
Photographs: Flickr or Picasa
Videos: DVD or Google Video
Documents: Google Docs
Email: Gmail or Yahoo Mail
Music: ? or CDs

SD card or external harddrive depending on data size

If you're a Mac person, use SuperDuper. Excellent backup proggy that creates bootable backups.