TYPO3 Related:
- http://www.typo3.org - Official TYPO3 developer website
- http://www.typo3wizard.com - Site with a lot of typoscript snippets
- http://wiki.typo3.org/index.php/My_first_TYPO3_site - Basic TYPO3 Knowledge
CSS Related:
- http://www.smashingmagazine.com/... - 53 CSS techniques
- http://www.w3schools.com/css/css_reference.asp - CSS Reference
(X)HTML Related:
- http://www.w3schools.com/tags/ref_byfunc.asp - (X)HTML Reference
PHP Related:
- http://www.php.net - PHP Reference & Info
Design:
- http://www.colourlovers.com - Colorschemes
- http://www.famfamfam.com/lab/icons/ - Free icons
Misc:
- http://www.apt-get.nl
- http://www.bulletgate.org
- http://www.ilovejackdaniels.com - A lot of cheatsheets on various programming languages and regular expressions can be found here.
Ajax:
- http://www.xajaxproject.org/ - The best PHP Ajax library i've seen.