When you're shooting in the rain (or other extreme weather conditions), there's a lot more to think about since cameras and water don't exactly mix well. An umbrella will protect your gear, but unless you have someone to hold it for you, it can be a pain to use.
Here's a simple (and cheap!) DIY umbrella holder by Digital Camera World that attaches onto your tripod so you can get those gorgeous rain shots—without having to hire a personal assistant.
All you need is two L-brackets, a flat piece of steel, a short piece of steel or copper pipe, and a few P-clamps. First, attach the brackets to the flat piece in a T shape. Separate your tripod head and screw the brackets onto the tripod head.
Attach the P-clamps to the section of pipe, then bolt it onto the bracket. Now, just insert your umbrella (preferably golf-style with a straight handle) into the pipe and you're done!