The single most relaxing thing I do with any regularity, just a few times a year: Sit on the deck, alone, in the dark, on the island. Just stare at the rocks, get lost in my brain. Works like a charm.
On a semi-regular basis, a long bike ride out in the sticks. Long shower afterwards, it all works out.
A cocktail or a few vinos is nice from time to time, but not expressly relaxing. The company and the conversation (or the book/newspaper/magazine I'm reading) are also quite important.
I also find that I can make private time for myself in a new place, with a comfortable chair, a newspaper, and something delicious to snack on. A beverage also helps. Had a moment like that, last, sitting on the roof of a hotel in Kuala Lumpur last December.
Jessie and I take a "flog ourselves to death" vacation once a year. This year we did a wonderful trip to Paris, crushed the museums, ate where we wanted to, up daily at 7am, in bed at midnight, and just drank in the city. I came back more relaxed than most anything else can give me.
Cheers,
-Andrew