When I was younger I had a camera that I didn’t know how to use very well, so I could never turn off auto-flash. Every picture I remember taking that had falling rain had used the flash, and there’s a ton of silvery-white drops everywhere. If that’s the specific effect you’re looking for, awesome, but I didn’t think it was very interesting.
http://ihasahotdog.files.wordpress.com/2008/04/funny-dog-pictures-alone-street-rain-storm-waiting.jpg
I see that pic a lot and while its a meme image, i think it does capture a good rainy day feel. Long(er) exposure shots might be neat to make the rain streaky instead of orb-like.
Coincidentally I just looked outside and the sun is shining, but its pouring rain. Oklahoma is so weird.