Anyway, whatever you've been fed about clothing manufacturers' geographic locales sounds like a crock. I mean, several prominent makers (not of bike gear, I concede) are in Seattle, near where I live, so it's not as if no one in the business knows about rain.
So, how to solve your problem? The first thing to do, of course, is minimize contact between moisture and you. If your bike doesn't have fenders, put some on at once. When it's raining, more than half the water that hits you and your bike is coming off the road, not from the skies. Then of course there's the issue of wet pavement when the rain has stopped—water will still roll up your tires and onto you.
As for your clothing, don't give up on rain pants—yet. Try some really light ones that are breathable and water-resistant, if not entirely waterproof. In this category, I'd take a look at some Concurve Profi pants ($99; www.gorebikewear.com). They use Gore's Windstopper fabric, which is more or less the same stuff as the late, lamented Activent that Gore quit marketing two or three years back. It's very breathable and repels lots of water, but eventually will allow some rain to get through. By then, though, you should be at work. Chances are, any true rain pant will just do what already has happened to you—condensation inside the pants will make you as wet as rain does.
The third step is to change your base layer. You don't mention whether you wear briefs under your cycling shorts/tights, but you should consider it if not. REI's MTS Midweight Briefs ($16; www.rei.com) would be a good choice—they wick well and are comfortable across a wide temperature range. Even better, I rate L.L. Bean's Polartec Power Dry Briefs ($15; www.llbean.com). I'm very impressed by Power Dry as a base layer. It wicks extremely well, so even if your butt gets wet—whether from sweat or rain—the moisture won't cling to your skin.
Keep the rubber side down!
For the ultimate road-cycling threads, check out the Essential Road Cyclist from Outside's 2004 Buyer's Guide.