www.sourceforge.com
Go into the PHP foundry or help wanted section.
Many people need PHP enabled websites for their project, you'd be doing them a huge favor.
There are many PHP projects to help out on, but many of them require a great level of skill, already. You might look at a project you find interesting and try copying just a small part of it. For instance instead of building a whole site, make a nice little news script with an administration interface. Try making a small calendar. Try keeping track of statistics on something and generating graphs and charts.
www.phpclasses.org also has a bunch of stuff you might try to do.
Go to www.xmethods.com and pick out some soap services (like mine :-) www.siliconllama.com/client ) and try to use them on your site to produce new content
make a function that will print any mysql query results into a nice table given the name of the database and the connection.
Make an e-mail form that sends nice content.
Make a poll.
