Oooo I can answer this one, I am basically addicted to money sinking hobbies...
Astrophotography - This is the most expensive one. I take pictures of stuff in the sky with a DSLR camera and telescope. Pretty fun hobby, have met a ton of cool people doing it.
Electrical Circuit Construction - I like to figure what makes things tick and use that knowledge to create different circuit designs of my own.
Speaker Construction - I research designs and either create my own variation on the speaker design, or modify it for my liking or the materials I have. I have made 3 sets already.
Fixing Shit - as related to the one above, I buy a lot of useless broken things on ebay/craigslist and attempt to repair them. Especially old electronics
Swimming - I have swam competitively since age 5 or 6, it keeps me in shape and helps some of my back problems.
Amateur Programming - I am by no means a good or seasoned programmer, but I like to create applications to simplify various aspects of my life.
Violin and Guitar - I am approaching my 10th year playing violin, absolutely love to play it every day. Still learning something and improving after 100s-1000s of hours of playing. As for guitar, I have played for 5 years and am improving at a slow rate. People say violin is more difficult that guitar due to the lack of frets, but the intricacy needed for guitar picking and strumming are something that I do not think I will ever have time to master.
I attached some of my astrophotography shots from 2012 or so, the skies have not been good enough to get a decent shot lately.
EDIT: I attached picture with a set of speakers I built in it.