MTG Price Gatherer is an extension for Google Chrome that populates MTG card prices from tcgplayer.com onto gatherer.wizards.com. It can be installed here.
chromegatherer is free and open source, and contributions are welcome! To contribute, please fork the repo, make your changes, then open a Pull Request against this repository. I will get to it as soon as I can!
chromegatherer is released and distributed under the MIT license.