When you have no choice but to ride in the rain to get home, you can't beat good quality rain gear, and a full face helmet. As much as I hate wearing a helmet, I carry a full face on road trips along with my rain gear just in case.
I have spent my share of time under bridges as well.

 

I have the Walmart camping rain-gear. It's done fine the 2 times I've actually used it in the rain. I started using the pants during the 50-60 degree rides into work instead of chaps or long underwear. They snap at the bottom so they're not loose and getting melted. So far so good. Now... if I ever did some cross country type stuff I would spend the $$$ on a good set of gear. I'm considering buying the face shield for my half HCI so I don't get stung in the face when it rains.

I hate rain.