Browser statistics – see how the world views your website...

http://browsershots.org – Browser appearance
http://www.w3schools.com/browsers/browsers_stats.asp – Most popular browsers
http://www.w3schools.com/browsers/browsers_display.asp – Screen sizes

Javascript & PHP

http://www.javascriptkit.com
http://jquery.com

http://rakaz.nl/2006/12/make-your-pages-load-faster-by-combining-and-compressing-javascript-and-css-files.html

Flash Authoring

http://www.entheosweb.com/Flash/default.asp
http://www.flepstudio.org

Regular Expressions

http://www.addedbytes.com/cheat-sheets/regular-expressions-cheat-sheet/
http://www.regular-expressions.info/
http://regexlib.com/

Video & DVD Authoring

http://www.creativecow.net/ – Great professional forum

Flash animation, impressive

http://box2dflash.sourceforge.net/ – very clever physics engine
http://www.jonathanyuen.com/main.html – artistic and charming
http://www.tokyoplastic.com/menu.html – kitsch and scary
http://www.onemotion.com/flash/spider/ – you too can own a venomous arachnid!
http://www.muxicall.com/ – piano simulator
http://www.theshadowfang.uwclub.net/splicer/splicer.html – fun for kids

Other Goodies

http://www.whaleofatime.org – organises creative workshops and events on environmental issues, also features the Whale of a Time Artist Community

http://www.thecreativebond.co.uk – graphics & motion graphics

http://www.thefirstpost.co.uk – general interest web magazine, featuring concise news and good visual arts coverage, including independent short films and graphic novels

http://www.wired.com – excellent tech magazine, not afraid of controversy, more hits than misses