Who doesn't love a spa day? Being pampered for a few hours or even a day is bliss. And a gift of a spa day is wonderful.
This is green because you are buying a sevice, which doesn't require wrapping! Plus, it helps the economy. Choose a greener spa, though I have to think most of them lean toward natural products. If it's your close group of friends, plan a day for all of you. It doesn't have to be on or around the holiday... make it for when the Winter blahs have gotten to everyone. The certificate can specify a date down the road that you can all agree on. It's a great thing to look forward to after the holidays. Or send your favorite couple so they may spend the day together. Or, just for the one person, if they could use some personal time. Even if it's not a spa, a gift certificate to a lisenced massage therapist is a very thoughtful thing. You can choose a length of time according to your budget. You never know... you might get someone hooked on your favorite therapist, and then everyone wins because they have a new client out of the deal.
If you're sure your gift-recipient won't be able to get away, or just doesn't like to have anyone touch them for that massage (???), put together a spa basket. (Yeah, there I go again with baskets. No, I don't have stock in a basket company.) Find nice natural spa products like bath salts and lotions and oils, and add some candles... maybe some incense... and put in a do-not-disturb sign for them to hang on their bathroom door, so your gift-person can enjoy a bit of uninterrupted "me" time.