This is a great article on getting a MEMP stack running on OS X 10.10 Yosemite:
http://blog.frd.mn/install-nginx-php-fpm-mysql-and-phpmyadmin-on-os-x-mavericks-using-homebrew/
Personally, I skipped everything with regards to phpMyAdmin, since I use Sequel Pro for interacting with MySQL databases. You may notice that there’s a known bug with the current stable version of Sequel Pro (1.0.2) on Yosemite, but if you don’t need user management, you’ll be fine.