Here's a few links I’ve found useful. All links include tool-tips for your convenience. :)

• Writing the perfect question (MUST READ FOR ALL NEWCOMERS)
• What have you tried? (Be prepared to answer)
• W3Fools (Please don't link to W3Schools in your answers)
• BookofZeus (Interesting articles)
• RegExLib.com (A bunch of RegExs)
• Random.org (TRUE random number generator using atmospheric noise)
• Handling UTF-8 with PHP (PHP specific)