Hot Scripts - this site has lots of scripts in both PHP and other languages as well as other programming resources. It is one of my favorites. It's categories make it easy to find what you are looking for.
Scripts.com - this site also offers scripts for both PHP and other popular languages. It has both free and commercial scripts available.
PHP Resource Index - This is one of the first sites I use to visit for scripts. It's been around a long time but is still a very good resource.
GScripts - this directory and free PHP scripts also includes a ranking system so you can see how well other users liked the scripts you are considering.
Site Scripts - this comprehensive directory of free and commercial scripts is easy to use and full of downloads.