2TB external hard-drive. I have 2 of them, one at home and one at work. I take my laptop back-and-forth.
I didn't back up for almost the whole year last year even though the HD's were inches from my hands. Lazy! Accepted an "upgrade" on-line from Apple and everything crapped the bed. Was able to get out of it without losing everything but usually don't let a week go by without backing up. Takes about 3 minutes if you are up to date.