Some online tools I've been using a lot lately are Writeboard, Mozy and yep...Gmail.
Mozy is a simple automated backup service which just runs in the background and backs up (just about) whatever you tell it to quietly and effectively. I have it set up to backup my entire (or just anything that's changed since last backup) writing folder nightly at 3am. It's free and encrypted.
Another thing I'm digging at the moment is Writeboard which is really just an online typewriter really. It's a page that you make a free document and just type whatever you want into it (with some limited formatting options) save and then you can access that document from anywhere as long as you have an internet connection and a web browser. You can even track changes and collaborate on the document with other people. There are other, better things like this out there but I like the simplicity of Writeboard.
I've been using it to write things while on the road or away from my main computer and to track my invoices to clients. Just remember to log out when you're done if you're using someone else's computer.
Another quick trick I've been doing lately is using a Gmail account I set up specifically for archiving files I need to keep around and may need while on the road. You have 2+ gigs of space at gmail and you can email files up to 20MBs in size so I'll just send off an email to this one account and then as long as I have a connection and a browser I can get the files from just about anywhere.
I have a flash drive in my pocket for stuff like this too but in case the computer I'm on doesn't have USB or doesn't like a Mac OS formatted drive or whatever, I can still exchange files with this Gmail account.
And here's a tip, make sure you see the "s" in https when you log into Gmail so everything is encrypted-ish.