Freelance writing is all about what you LOVE. Everyone loves something, even if it's only pizza. The problem with the stuff you're most in tune with however, is that it's so much a part of you that you may not even see it.
What do you do to goof off? Do you play computer games? Do crossword puzzles? Veg out in front of the TV? Play golf?
If you love something, others love it too. For example, for a time I was addicted to crossword puzzles. Unfortunately the addiction passed, so I never followed up on it as a market for my writing, but I know that I could have.
What's your favourite vice? Or virtue? Write about them.