I ride in the rain probably 50 degrees F and higher. I'm enough of a cold weather wimp in the winter without the rain.
I love rain in the summer. I love those random thunderstorms that happen on the really hot days. You never know when or where they'll pop up, and when they do it's a welcome break from the heat- almost like riding into a lake. Haven't you ever ridden by a lake on a hot day and thought, "Man it would be nice to jump in that lake right now"? I love that smell in the air right before it rains, and the calm after a rain storm is a beautiful thing to ride through.
I've said it before, but I was one of those kids who wanted to go out and play in the rain, but my mom would never let me, and I think that's one of the reasons I like riding in the rain so much.
Anyone who's never ridden in the rain and/or in the dark is missing out!