DropBox is a great way to backup important files. Once installed, you simply drag your files to your dropbox folder. You can access your files via a web interface, or by installing DropBox on other machines.
DropBox gives you 2 gigabytes FREE storage. You can pay for more storage as required.
Check it oou HERE
With the ever growing switch to 'Cloud Computing' becoming an increasing part of my workflow, I'm kicking myself that I've only just started to take bookmarking Delicious seriously.
I was using an online bookmarking service called 'Homepage Startup', however, whilst it is a great service, it is run by a bloke in LA, and the service can go down if for some reason he doesn't pay his monthly GoDaddy bill.
I've been without my 'Cloud' bookmarks twice now for over 2 weeks, which is a pain in the bum, and I've heard Leo Laporte and Merlin Mann talk about Delicious a lot on Leo' Macbreak Weekly podcast.
I signed up and BINGO. I exported all my Safari bookmarks to Delicious, along with TAGS that make it easy to organise and find bookmarks in Delicious. I've also installed plugins for Firefox so I can bookmark easily on the Windows machines that I use.
Check it out HERE 
Stumble Upon is a great site where you sign up, log in and select subjects or genres that interest you.
You then click the 'Stumble' button, and you are taken to random sites that meet the criteria you've entered.
You can add sites that you really like to your Stumble Upon favourites, or bookmark them as you normally would.
Check it out HERE 
Backup