Your hard drive is full. Normally that isn't such a big deal, but what if you need to grab a coworker's files before she leaves for a vacation, or what if you want your massive overnight file download to go off without a hitch? Here are some short-term tips for clearing space on your hard drive until you have the time to do a proper cleanup.
Hard-Drive Spring Cleaning
Before you do anything else, empty your Recycle Bin by right-clicking on it and choosing Empty Recycle Bin. Even the most hardened Windows veteran can occasionally forget that they left a few DVD images in there.
Firefox: Go to Tools, Advanced, Network. Click the Clear Now button to clear the cache, and adjust the amount of space that the cache uses down to what you can spare.
Safari: Enable the menu bar (click the gear in the upper-right corner and choose Show Menu Bar) if you haven't already. Then choose Edit, Empty Cache.
Google Chrome: Click the wrench icon in the upper-right corner, and go to Options, Personal Stuff, Clear Browsing Data. Here you can check what kinds of data to delete; check Empty the Cache and select Everything from the drop-down menu.
Find More Disks
Even if your hard drive is full, you probably have a handful of other disks that you can temporarily draft into extra storage duty. Obviously, other computers on your network can pull their weight, too; but if you're in an office or school environment, you might have access to a network drive for storing some stuff. Just check with a system admin to make sure it's okay before you start any file transfers.
Also, you likely own a handful of other devices that could help: A portable media player, a flash memory card, a USB thumb drive, or even the internal memory of a camera or phone can mount via Bluetooth or USB and act as a removable hard drive. Keep note of where you're storing your files, though, or you might find yourself missing something important later on.
Don't overlook your humble optical drive, either--any remotely recent computer should be able to burn CDs and DVDs, and even when most stores are closed you can still find blank optical media at an all-night pharmacy or convenience store.
If you don't have enough local storage, you can try to keep files on the Internet. Online storage services such as Box.net can provide you with an extra gig or two of storage space if you're willing to put up with the hassle of uploading and downloading your files. Also, Google recently expanded its Google Docs app to allow users to store any file up to 250MB, with 1GB of total file storage for free.