Get some online backup this holiday weekend!
So during this long weekend, why not set up one (or more) of them? (Note: Most of these links are referral links - which usually get me, and often you as well - extra space on the service.) While each has their strengths, keep in mind that you can use them all!
Box.Net (now just Box) has 5 gigs of online space, which you can mount as WebDAV. (You might know this as "web folders".) This makes it pretty easy to move stuff back and forth as if Box was just part of your computer's hard drive. It has a pretty straightforward mobile app as well, but its strength is with your main PC - though this guy uses it with his iPad and Pages. If you've ever used a network drive, this is the experience I tend to have with Box.
Dropbox has 2 gigs of online space for free, and pay accounts for more. The mobile app is spiffy, and there's lots of integration with other mobile applications. If you're looking for a mobile-access site, this is the one you want. Seriously. You can increase your space by referrals; be sure to associate an .edu e-mail address with it for a student bonus with each referral! When you sign up through a referral link, you should get extra drive space as well.
Min.us is the new kid on the block. It starts with 10 gig free space to start out with. They focus on a clean, clear interface - it's the only one of the bunch where I actually like the web interface. Min.us is strong when you want to share things (either publicly or with selected people). Their suggested uses include: Create an online portfolio of your work, share photos and videos, publish your work whether it's an ebook, music, photos and more, share lecture notes with your class, share anywhere via the browser, desktop and mobile. Like Dropbox, referrals get both people extra space on the service.
SpiderOak, however, is the cross-platform secure backup solution for me. The service isn't speedy, but that's not what it is meant to be. It is all about keeping your data safe and secure. While there are sharing solutions, its strength is backup. On top of actually saving your files, it has some robust versioning - that means that you can go back to an earlier saved copy. It also has the largest referral bonus (for both parties) - one gig per referral. Starting at 2 gigs free, that's not bad at all. SpiderOak has personally saved my bacon more times than the others combined.
If you've used another service that you'd recommend, post about 'em in the comments!