Right now, and for I don't know how long, you can get one year of the CrashPlan+ Unlimited service for free:
I keep a list of online backup services and for the moment, CrashPlan tops it. It's inexpensive (even more so, right now), it's unlimited, and it's fast. This is the service I use at home.
PLEASE NOTE that the small print says you must be a current Carbonite customer though I'm not sure how they know that when you sign up. I do know that this offer doesn't apply if you're a current or former paying CrashPlan customer. Of course be sure to read the Who is eligible? and the Terms and Conditions links that are on their sign-up page.
This particular CrashPlan+ plan usually runs $49.99 per year. See my Unlimited Online Backup Price Comparison table to see how CrashPlan+ stacks up against the competition even without this first-year discount.
Thanks for the heads-up Mark!