Cork and bamboo are among the most eco-friendly choices, according to FloortoCeiling. Per a company press release, cork trees don't have to be harvested -- only the bark is removed, and it grows back. Cork is also relatively inexpensive, with prices starting at less than $3 per square foot. But since it is a softer wood, heavy furniture can put dents in it.

Bamboo is another good choice because it grows much quicker than wood, and it looks great too. It can be cheaper than hardwood too.

And another option is one that I wouldn't have necessarily thought of as sustainable -- linoleum.

Floor to Ceilings' Bob Kilbury says "Linoleum is less resilient than vinyl, but produced from renewable materials, such as linseed oil, rosins, wood flour, jute and pigments that are ecologically responsible."