Manila folders. You don't want to live with them, but you can't live without them. You could spend extra on a set of pretty (but pricey) pre-packaged folders from a big-box office supply store. Or you can re-cover the inexpensive, boring ones you've already got with a new, fresh face.
The Easiest: Washi Tape (shown above) Here's an easy style upgrade for vanilla manila file folders: labeling and decorating with strips of patterned washi tape. Just stick a short strip on the tab of each folder, then apply a clear printed label on top. You can even use the colors and patterns to help sort your files by section, like Samantha of Simply Organizeddid.
The Brightest: Contact Paper
If your files are on display, consider transforming their bland beige exterior with brightly colored contact paper. Megan of The Homes I Have Made covered her family's command center folders schoolbook-style with yellow patterned contact paper.
The Coolest: Vintage Fabric
Just a can of spray adhesive and some careful cutting can transform boring manila into something brilliant. Use vintage fabric, like blogger Katherine Jalaty did for this post on Design Sponge, to cover the outside of your folders for great texture and an awesome look.