If you have a large group of files to transfer from one computer to another, you can do so with Dropbox — even if the total size of the files amounts to more than your free Dropbox space.
Say you have a large group of documents, music files, videos or anything else, and you want to get them from your home computer to your work computer. If the group of files exceeds your Dropbox's free space, you can still transfer them all with some automatic folder actions. Just create a folder in your Dropbox specifically for transferring files (I've called mine "Transfer Queue"). Then, you can set your computer to automatically move files out of that folder when they finish transferring. If you're on Windows, you can use our multi-talented file organiser Belvedere, and if you're on a Mac, you can use an Automator folder action as described in our mobile Dropbox printing guide (just create a folder action containing only the "Move Finder Items" action).
When you want to transfer the files, you can just drag them all into the "Transfer Queue" folder at once on your home computer. Dropbox will begin transferring them to your work computer, and when your work computer receives them, it will move them out of your Dropbox, making room for the others to be uploaded. You'll get a lot of "Dropbox Full" errors from Dropbox along the way, but you just need to give it time — once it finishes downloading a file on the receiving computer, Dropbox will continue its way through the queue.
It won't work in every situation (like if any individual files have a file size larger than your Dropbox's free space), but it's a handy way to get a large group of files from one computer to another without using an external drive. It's also especially nice if, say, you don't have the time to wait for those files to transfer when you're actually at your work computer — you can let them copy overnight while you're at home and they'll be waiting for you the next day. Thanks to Robert for figuring this out!