Well I thought that I would make a list of some of my favourite resources 
General Wow Resources
wow.com
Well this is a given really, regular updates from people who are in the know (is that even the right term?)
World of Matticus
http://www.worldofmatticus.com/
A lot of interesting blog entries from a wide range of writers.
Addon and Mods
Wow Interface
I wide range of addons (including my own oUF layout haha), my only gripe is it is not the best looking site and can sometimes be difficult to find what you want. Navigation and browsing is not very user friendly
Curse
Easy to use addon side but really pushing their own paid services (which turns me off) but they do have the benefit of owning wowace now and so Ace Projects will generally be published through curse website (sometimes exclusively).
Vranx
I found this the other day and is a great strating point for those looking to start modifying their UI, has a lot of information about different options you have for various aspects of ui mods.
NoStockUi
Great site with lots of people providing comments and feedbacks, sometimes I get frustrated by the delay between posts but Matt is a busy person
Character Planning
Wowhead
Has a lot of really cool tools to give you a list of possible upgrades e.g. http://www.wowhead.com/?items&filter=ub=11;gm=4;gb=1;wt=61:123:24:23:96:103;wtv=100:53:48:28:14:12
Wowhead Profiler
http://www.wowhead.com/?profile
Great profiler for checking gear and stats etc.
Wowheroes
Great profiling and gear checks, also includes achievements and raid history.
