I always leave my porch light on now.
[Edit, 11/23/07: Apologies to everyone I worried with this post. I was perhaps feeling a little melodramatic. :) It was brought on by a break-in that happened at my house in October. I didn't talk about it specifically here, but two posts were fingerprints the police found and the window that was broken. Nothing new has happened, but I do always leave my porch light on now, and I am always scared of what I'll find whenever I pull into my driveway.]