Jonathan at DivisionByZero wrote up a nice article about some sites & strategies PHP devs should know about.  Especially those new to PHP development.

http://www.divisionbyzero.co.uk/2010/08/09/6-must-see-sites-programs-articles-for-learning-php/

I especially agree with the PHP Manual.  PHP is highly community-driven, and the manual shows that.  Almost any function you search for in the manual, you’ll see a ton of community comments relating uses, caveats, etc.  I’ve been working with PHP for many years and I still hit the manual probably twice per week.