Well, here are some obvious ones, but some really good ones too..
www.google.com
- of course!
www.dictionary.com
- I find this very useful
http://www.economist.com/research/StyleGuide/
- Learn yourself gooder English
http://www.askoxford.com/
- Ask Oxford anything about the English language
http://www.howstuffworks.com/
- Fun site which can be very interesting sometimes
www.webopedia.com
- Simple site that is sometimes usefulu for quick technical term look-ups
Cool thread...
Mr Mephisto