I get stuck in the rain all the time. Just my luck. I don't plan on it, I don't like it, I don't want to, but it never fails that I'm 500 miles from home and the heavens open up.
The one piece rain/motorcycle suits like Gary mentioned are awesome for long trips but kind of impractical for every day. However they do offer the best protection. Problem is, they are harder to store on the bike, not always practical, and while they certainly help if you're packing for a trip or heading out on a rainy day, they don't help if you're caught in the rain and you had to leave them at home. BUT, if you have enough room on the bike to store a good one piece rain suit? GO FOR IT! Just make SURE you get a motorcycle-specific rain suit that has heat protection in the legs. It's worth the extra money. It's bad enough to melt your rain suit to your pipes, but you don't wanna be those guys whose rain suit and flesh become one! Just spend the extra and get the ones treated for high heat on the lower legs, cuz in the wind and rain that material will flap around and touch the pipes. Here's what I do;
I have a Fieldsheer jacket with armor, and a rain liner. Rain liner works great. Now, a jacket with a liner will get HEAVY in the rain, wheras a rain-jacket won't because it won't get wet! The rain liner stays dry, the jacket gets soaked. But it doesn't bother me.
Tourmaster overpants, they do a great job of staying dry in all but the most insane downpours.
Scotchguard spray on the boots
Gloves I haven't figured out yet. Got some thinner leather gloves that work pretty good, though of course leather eventually saturates with water.
Full face helmet a must for riding in the rain, IMO. There are lots of great gloves with a 'visor wiper' to wipe the rain off of your visor.
Also; one thing I found- those cheap little plastic ponchos you can get at wal-mart work wonders in a pinch. Believe it or not, the 2 or 3 dollar ones that are made of heavy plastic don't work at all- they just blow up in the wind and make you look like the stay puft marshmellow man. But the thin cheap ones made out of super thin plastic work great. Like 89 cents a pop. They are so thin they cling to you and don't ride up or blow up with air. In a pinch, they work well. I always have 5 or 6 of them on my bike, along with disposable hand warmers and boot warmers. When you're out riding with unprepared buddies you can pass it out and keep them better. And if you just happen to be out and the rain hits and you don't have your rain gear- they are small enough to squeeze and fit on the bike and have them there 24/7.
I have one saddlebag dedicated to 'incidentals', it's always packed. Among tools and first aid stuff, I have;
A T-shirt, sweatshirt, socks and a pair of gym shorts. If you get caught in a sudden harsh downpour and don't have your raingear, it can be really miserable to ride in wet clothes. Having the extra T-shirt and stuff I can change and be dry, and throw the sweatshirt on because it's usually cooler when it's raining.
I have my rain liner, folded up. The aforementioned ponchos, and 'hot-hands' hand warmers and boot liners. I also have a pair of heavier leather gloves.
Also, check this out;
That jacket (and others like it) have the 'RainGuard' features that my pants have, and let me tell you it works! The pants are thin and breathable, and you can feel air flow through them, but not a drop of water gets through them. I waded out into a creek once in my riding pants and it took 3 or 4 seconds before the water started to trickle in. I think I read somewhere the fibers swell up when they get wet so the water can't get through? I dunno, some sort of something! But it works. If you are the type that wears gear all the time, that may be the best solution of all, because it's thin and light gear you'll always be wearing, and you'll ALWAYS be waterproof. If it starts to rain you just keep riding!
Worst I've been in is actually a tornado. My buddy and I went riding, one of those classic scenes from a movie where the forecast changes as we walk out of the door. Calling for some thunderstorms early the next morning (like 2AM). Well, unbeknownst to us, it changed to 5PM. So, 5PM rolls around, we're 300 miles from home heading back, starts to rain, then storm. We pull off, get our rain gear on, starts storming like the dickens. We're riding down the interstate about 45mph, noticing that there are almost NO cars on the road AT ALL, we get pelted with hail, debris from trees start to fall. We pull off and see that this was the tip of the storm, moving about 30-40 miles an hour, and it was one bad mama jama comin up. So we decided, the best bet was to keep riding along the tip of the storm, and not wait around all night for it to get bad. In retrospect? A motel would have been a better choice, had we known. Anyway, storm picks up speed (again, we had no idea) and catches up to us. Hail and debris like crazy. We get to my house (he was another 20 minutes away, gonna wait until morning), and we start watching the news about a tornado that touched down right where we had ridden through, probably 5-10 minutes after we rode through it.
Moral of the story? Pay attention to the weather and don't mess with the storms. But, we thought we were smart, turns out we weren't. Made it out alive but what an eery experience. Everyone ELSE, with their car radios and not-dumbness, knew how bad the storm was and was gone. Kind of eerie when it's 5 in the evening in the summer, pitch black, and not another soul on the road as you and your buddy are riding along the road!