I could not get PHP for the longest time, and got an error about not finding the mysql socket, as did another user who commented on this list. This is how I solved it.
I got a php.ini file from a PHP installation on the Web. (It seems OS X doesn't come with one.) If you know a friend who has one, borrow his or hers.
I put the php.ini file in /usr/local/lib. I then searched for the line mysql.default_socket and set it to this:
mysql.default_socket = /usr/local/mysql/run/mysql_socket
My MySQL installation houses its socket there. (I had installed it from the instructions at Apple's Internet Developer site.)
If I remember correctly, that was all there was to it. PHP could access MySQL after that :-)