Xenon has been the gas anesthetic of the future for a long time now. It does have one set of good qualities: it's not halogenated (like all common gas anesthetics), but it's nonflammable (there are very good anesthetic gases, like cyclopropane, that are extremely flammable and have thus been totally phased out of use), and because it's such a heavy atom, it essentially never leaves the atmosphere - no matter how much you use, you can always recapture it from the atmosphere.

It's not particularly cheap, though.