I collect model horses, I'm starting to collect dog collars (how can you just get one?), bandanas (for the dogs). . .and interesting gems and rocks.
My biggest collection, though, is books. I love books of all sorts.
Some hobbies are reading, writing, drawing, art projects (like collages and things), listening to music, playing guitar (though I don't do it consistently enough so I forget things and regress), and I'm really getting into photography.
I also love horseback riding- anything do with horses, really, and hiking and things like that.
And I really, really love learning. Anything. I devour books and look on the internet for random things and things that strike my fancy, I have lots of lists of vocabulary words, and on.