About five years ago, I worked in an art gallery that was outfitted in Knoll shelves, filing cabinets, and task chairs, and I still miss that space. Knoll's furniture is simple, which can make it seem unreasonably expensive, but its real value appears over time, when you watch it improve with use. The Knoll filing cabinets at that gallery were some of the most basic ones available — they were modular lateral files made from metal — and over the years, the glides eased deeper into their grooves, the drawers seemed to roll more easily and quietly the longer they were used, and the surface of the cabinets grew richer with every ding, nick, or hand-worn edge. A single, three-drawer file cabinet can cost you more than $2,000 (which is admittedly more than an average person can afford for a file cabinet) but you probably won't need to buy another one for 25 years or more.
Knoll follows strict environmental production practices, they're agressive about third-party certification, and many of their products are certified by the FSC (Forest Stewardship Council for wood), SMaRT (Sustainable Materials Rating Technology for products), LEED (Leadership in Energy and Environmental Design), and GreenGuard (Indoor Air Quality monitoring). They also participate in Full Circle, a resource recovery program that resells, repurposes, recycles and/or converts products to clean Energy-from-Waste. For our money, however, the greenest thing about their furniture is that it's made to last so long.