One of the single best things and single worst things about PHP is the PHP Manual.
It's complete, is always up to date, specifies when commands became available, and has a huge amount of commentary and tips spanning the past few years. Quite often I get more from the comments than the actual entry… There are parts of the Manual that I use far more than any others… like the formatting parameters that date() takes. I remember the basics, but it seems that I almost never use the basics. I use this page so much that it's always in my browser history and I've considered adding it to my toolbar.
Unforutnately, the downside is that unless you know the keywords or related topics that you're looking for, you don't have a chance of finding it. The onsite search is sufficient for exact/partial terms but mediocre at best for anything close. A long time ago, I gave up and relied on Google for that heavy lifting.
Well, due to the brave efforts of one of the DCPHP'ers – Jason Lefkowitz – we have an alternative in MyPHPDocs.com. The site lets you click and drag the portions of the manual that are the most important to you, hit a button, and voila. You have your own manual. The best thing is that the tool isn't copying content from the site. You don't have to worry about getting out of date because it effectively acts as a page of bookmarks to the core manual.
After poking around with it, you'll realize that you have even more. Every new manual gets rolled with the FAQ and the various migration guides. You can basically treat this as a quick table of contents and have everything you need just a click away. After using it for a couple days, my manual was added to my Toolbar.
If you have feedback, drop Jason a note. There's a feedback link at the bottom of the site.