Absolutely. You can almost always sell any green item for at least 1 gold, because somewhere out there is an enchanter in need of magic essence or dust.
On my server, selling greens tends to be hit or miss, but stuff for tanking classes (mail or plate of the Bear, typically) regularly goes for 5 to 10 gold, and I see Agility gear (Monkey especially) going for anywhere from 20 to 50 gold, especially if the required level is 16 to 19, as those are good pieces for PVPers.
Once you hit 60 and you start venturing into Outland, vendor prices become extremely reasonable; it’s not uncommon to be able to sell an unneeded item for 6 gold or more. However, reserve that for quest items you can’t use, as you can still probably get more on the auction house for bind-on-equip greens you find there.
At the end, though, the market for mid-level greens is relatively pretty small. A lot of veteran players don’t bother with gear beyond what they can get from quests or instances, because they’re eventually just going to outgrow the gear and thus it’s a waste of money. I still like to trawl the market occasionally, in case there’s a really good deal on an item I could use. I recently bought a Twilight Armor of Intellect (cloth, +17 Intellect, level 35 required) for my mage, who’s only level 12 right now. It was only 6 gold, and it’ll be extremely useful to him when he hits 35.