The very first is music in all kinds, especially I enjoy improvising on my classical guitar. Also try to learn piano from time to time.
Computers. I started to use computers on the very beginning, in high school by constructing electronic circuits based on Z80 microprocessor and using assembler as programming language, later on university had occasion to learn higher level programming languages. Now I use mostly Java for all kinds of development.
Traveling - quite many countries visited so far and several states in USA. Since I came to US I enjoy driving in nice environment areas like mountains in California, Colorado or Yellowstone.
Sports. Skiing - started to learn a few years ago, swimming, hiking - just moved to Colorado and love it, sailing - maybe some day I will try that on sea.
Psychology/Philosophy/Religion - I try to be open to unknown. There is a lot to explore here however not necessary to talk about. One of the topics that returns to me from time to time is Lucid Dreaming, it has happened to me several times and always produced plenty of vital energy.
Science - enjoy following news about latest technology advancement and new inventions. I used to work on University and now I miss scientific research work a little.
Books - I have always been reading a lot. I like libraries and enjoy finding inspiration and new knowlege in books.
Spoken languages - since I came to US, English language became reality on every day, but there is still a lot to learn. I arrived to this country with very basic practical knowledge and almost no experience in verbal communication. Now it has improved greatly. I even started to learn Spanish, it is surprisingly easy with course by Michel Thomas.
Electronics - I have good understanding of electronics, I even had one commercial electronic hardware project many years ago, it was a PC card for controlling industry machine behavior (motion, temperature etc.). Now it's just a hobby, see biofeedback.
Economy. I am not sure if this is still a hobby. In 98 I did my second master degree in this field, it was interesting at that time. Since then I have not had occasion to try this knowledge in practice, only minor funds operations like stock exchange or banking.