I've just started my tutorial site which is in my sig, hopefully it'll help eventually, but until it gets full of tutorials try tizag.com to get the basics, if you need any help just make a thread here or PM me and I'll make a tutorial =] Dan
Most popular and good ones are php.net and w3schools.com When you are done with some basics you can get some very good php scripts and tricks on my blog about php which is http://codingtricks.blogspot.com I also covered topics about user management and authentications and scripts for all kinds of emails.