Here are the two we like the best.
The first is a happy sun, coming out from behind clouds. I like this because it's positive, and actually relates to the function of a weathervane. In life I always try to find the good behind the not-so-good --like SpongeBob -- and this weathervane reminds me that there is a silver lining in every cloud. The sun also symbolizes successful ventures, which is always a good thing.

The second is St. Michael and the Dragon. I like this one because of the association with fire. Each hobby that is going to be present in the cottage deals with fire. Michael is the archangel of the South, the direction associated with fire. I guess if there's a message it's the triumph of good over evil.
Another design we thought of was a phoenix, but I'm not so keen on putting a bird that is burnt up over and over again on top of a building that I'm hoping never burns down.