This is a fun question to answer because the alternatives to paint are nearly boundless. You could consider wet-applied products such as plaster, glazes and stains; adhesive-applied products like wallpaper and textiles; or even hard surface materials like wood paneling, stone veneer or tile.
Whatever wall covering you choose, be sure to use low- or no-VOC glues and sealants. Most textile or paper wall coverings have a backing of some sort in order to "take" the adhesive. Paper is commonly used as a backing; choose paper and avoid PVC/vinyl.
Wet-applied products. Plasters are rich in color and can be beautiful, provided the application is done by a skilled worker. For buildings constructed of alternative materials like rammed earth and straw bale, plasters are a natural choice. Select lime- or clay-based plasters and avoid petroleum byproducts or cement-based plasters (cement manufacture is an energy-intensive process). Some clay plasters contain paper, stone, sand or other additives for a textured finish. Although some plaster finishes can also be painted, plaster with integrated colors is more attractive.
Adhesive-applied paper products. Adhesive-applied products hearken back to the '50s and '60s, when PVC-coated wallpaper was a decorating staple. Today, there are still many types of wallpaper on the market, but the patterns are updated for the times and the options are greener. One fabulous choice is Mod Green Pod, which appeals not only to green sensibilities, but to a modern, fresh design aesthetic. The silk-screened paper is PVC-free, with water-based dyes and coatings, and the manufacturer claims that it can be wiped clean with a sponge.
You could choose wallpaper containing recycled paper, such as Pallas' Dialtones line, made of discarded Japanese phone books. MIO's PaperForms 3-D wallpaper is made of post-consumer recycled paper; it has acoustic properties and can be painted.
Textile wall coverings. Many upholstery manufacturers are getting on board with new developments in green textile wall coverings. (Some of these products are only available to the trade, if you are working with an interior designer.) Maharam's Natural line, for example, includes coverings made of cellulose and polyester. Pallas Textiles Natural line includes stone, straw, bark and wood pulp in the matrix, along with rayon, polyester and linen. These wall coverings have a sometimes subtle, flecked look in a minimal number of colorways that can convey the "natural" concept, but can also be paired with modern furnishings for an updated feeling. Allegory, from Innovations' Innvironments line, is a polyester- and wood-based textile wall covering that comes in solids or prints but can have a more institutional or commercial look. Yet another manufacturer is DesignTex, which makes a Duraprene wall covering containing latex and wood pulp. This product is designed for easy cleaning?you can scrub it without rubbing off the pattern.
Hard surface materials. Another fun option for walls is cork, which has the added benefit of absorbing sound. HabitusNYC makes a cork mosaic pattern that can be used on walls. Cork's aesthetic is earthy and natural, but the disk shapes in this pattern lend an unusual and modern flavor.
One last thought: Don't be too quick to write off paint. A thoughtfully designed decorative paint application (using low-VOC paint, of course) can really transform a space by making certain planes "pop" boldly or recede with subtlety. There are many websites and books for do-it-yourselfers about the power of pattern and color in room design.
For more information:
Read more about green paints and coatings in GreenHomeGuide's Paints & Coatings Know-How section.