Start with my favorite: http://zhongwen.com/
Based around a really handy family tree dictionary of chracters. The Chinese FAQ has some really interesting little essays. There is a huge list of links. They may be a bit out of date now,but are pretty extensive. There used to be a forum that was once quite good but it’s closed now which may not be a bad thingbecause it was getting quite pathetic last Ilooked.
http://ocrat.com/chargif/
Animated Chinese chracters. Good to show you howto write - order and direction.
http://www.chinalanguage.com/index.html
My favorite online dictionary. I have used this to refer to Chinese characters in discussions with people who don’t have Chinese software. Unlike zhongwen.com every character has it’s own adress to refer to each character. You can alsouse the 4 digit unicode number and look upby that, so I can just tell you that the chracter I’m referring to is shu (8853)
One that I’ve been using a lot is the on-line Lin Yutang off the Chinese University of HK site. I think there’s a print version that’s more up-to-date, but the online one is still useful (humanum.arts.cuhk.edu.hk/Lexis/Lindict/)
More specialied are the dictionaries posted by Charles Muller (acmuller.net). This includes both a literary dictionary and a dictionary of Buddhist technical vocab. The Buddhist dictionary is the largest of its kind anywhere in any format.
My two favorite online dictionaries are the Lin Yutang dictionary mentioned by Grizzly, plus a humongous Chinese-Chinese thing called guo2 yu3 ci2 dian3, which you can find at http://www.edu.tw/clc/dict/
Ironlady mentioned an interesting program in another thread:
“Bamboo Helper which will automatically segment any Chinese text file and give you a list of the words unknown to you, with their English translations”.
They have links to different Chinese dictionaries as well as discussion boards with quite a number of topics on Chinese language, Cantonese, Minnan-Hua and Hakka (as well as the ubiquitous requests for the translation of English names and the perfect tatoo :?).