I love the rain, especially during the summer. The interesting thing about living in Wisconsin is that you can go weeks without a decent rainstorm, then you'll suddenly get torrential downpour, seemingly out of nowhere. I decided to grab my camera and photograph some plants after a particularly heavy rain.
Part of my motivation for doing a shoot in the rain also came from reading a National Geographic article by Jim Richardson. Specifically, his suggestion to use a little bit of flash, about -3.0 stops, to make the raindrops pop. You might have to have an external flash to do this but some cameras let you adjust. I use a Nikon D3100, and it let me do just that.
Also, I'm not sure how everyone feels about photoshop, but I like to use it to some extent. For the most part I just play around with the saturation and definition adjustments in iPhoto; I think it brings out some of the finer details on object surfaces.
Jim's advice appears to have worked, from what I can tell. I highly suggest getting some shots in the rain as there are a lot of great details you might miss if you don't snap a picture. Also, if you have any good shots in or after the rain, lets see 'em!