I think the most popular guys out there is SWIMS
http://www.swims.com/
https://www.google.com/search?q=swims+overshoes&ie=utf-8&oe=utf-8

But they're probably on the higher-end price wise.
they offer a range of colors.

that said, there's no reason you can't get a lesser known, and much cheaper brand. especially if you're going to get them in straight black.

i don't own a pair of overshoes myself, but i certainly thought about it back when I had to go to the office on a wet day.