I have a Mac so I use Apple's Time Machine, which automatically backs up my HD several times a day. I can also restore my Mac from a previously-created backup, which was really handy when I replaced my Mac's stock 5400 RPM HD with a new solid state drive.
For other files I know that I'll need, I throw them on Dropbox so I can access them at my office or on my smartphone.
Google Drive (nee Docs) will automatically backup designated folders now. There's a client to download that will take care of it for you.
While you're at it, the Google Cloud Connect plug-in allows you to save, modify, sync, and share Microsoft Office files in native format. If you're working offline, you can sync your changes to Google when you're back online; and if others alter a file, you can control whether yours should supersede others' changes.
Very easy backup utility that runs in the background, and good web interface for looking at your data. Thankfully I've never had to recover anything from them, but they have good reviews from people who have.
One of the nice things about it is that you can also back up locally.
harddrive with its own back up software. It backs up my files at a preset time each day. Since you don't want a hard drive sitting around, I don't think it's really needed. For me, it's nice too have both; but I am a one person operation. So, I don't worry about the HD sitting around.
I use Carbonite as my cloud backup. I prefer Carbonite because I can click on the specific folders that I want it to backup. It monitors in the background and when you save a file, it immediately queues it up for a back up. It does not interfere with the rest of the computer. Since I do a lot of computer work from 9am-Noon (with more appointments in the afternoon), I have set Carbonite to hold off on backing up between 9-12, just to make sure there is no interference. I have Carbonite app on my iPhone, iPad, desktop and laptop so I can access the back up copies from any other them. I spend about $90 per year for Carbonite to backup my desktop and the Seagate HD, described above.
Carbonite also has a Mirror feature that will keep a Mirror image of everything on your computer. But, you need a separate HD for it. I have not used it. But, a IT tech used it to seamlessly replace my desktop hard drive.
Dropbox is nice, but you need to set up a new Dropbox folder and slide your data storage folders into it. I did not want to worry about that, especially for actual program features. WIth that said, I also have Dropbox on my machines since it is a great way to save a file on one machine, and make it instantly available to the others.
I only use it for docs, pdfs, and pictures from my mobile phone. They give 4GB free and I have no complaints so far with 6 months' use.
I was periodically backing up to an external hard drive that I then stored in a fireproof, waterproof safe (in the event of a catastrophe). The problems were: I had to remember to do this, it was (obviously) a manual process that was fairly time consuming (I back up all music, video, and photos), and files created/modified between backups were at risk in the event of loss of some sort.
I have since installed a backup drive (Drobo) that stays put at the desk and subscribed to CrashPlan for online backup. It runs $50/year for unlimited storage space for 1 computer, including any attached drive. Like the poster above, you can set it to perform backup during non-peak hours, so it is pretty foolproof once you get it set up. As with Carbonite, you can choose specific drives/folders/files to backup.
I have about 2TB of photos local. I back them up to a second 2TB drive and an external. I shudder to think it might take 6 months to upload that stuff.
I receive an email update each week indicating the number of files and total size of the data uploaded each week. It varies from 90GB to 200GB per week, so on the low end, 2TB could take up to 6 months. Users have reported timeframes as low as 6 weeks for just under 2TB, so your mileage may vary.
up something like 20,000 songs for free. It's what I use for my music files. It syncs too, so the only thing you need to do is make sure your music is in the right folder.
similar ones. Google Drive, Box.net, Amazon Cloud Storage and Microsoft Skydrive. I use Skydrive to back up my photos as I got in early on it and got something like 20 GB free. I think it automatically syncs folders, similar to what you describe with Carbonite. I don't think the others do that automatically. I think right now Skydrive is offering 7 GB for free.
I use Google Drive for pretty much all the documents I want to save and sync. It's nice to be able to edit almost anywhere from a browser.