• Cambridge Dictionaries Online
  http://dictionary.cambridge.org/
• Merriam-Webster Open Dictionary
  http://nws.merriam-webster.com/opendictionary/
  
• Wiktionary
  http://en.wiktionary.org
• The Online Slang Dictionary
  http://onlineslangdictionary.com/
• A Dictionary of Slang
  http://www.peevish.co.uk/slang/

• 字典網
  http://zhongwen.com/zi.htm
• 成語典
  http://dict.idioms.moe.edu.tw/
• MDBG Chinese – English Dictionary
  http://www.mdbg.net/chindict/chindict.php     

Putonghua

• 普樂網 (ILC)
  http://www.ilc.cuhk.edu.hk/Chinese/plw/intro/_home/home.html
• Everyday Chinese (ILC)
  http://www.ilc.cuhk.edu.hk/chinese/re_PTHforForeigners.html

Cantonese

• 粵講粵啱一分鐘
  http://www.rthk.org.hk/elearning/bettercantonese/index.htm
• 粵語審音配詞字庫
  http://humanum.arts.cuhk.edu.hk/Lexis/lexi-can/
  
      

• Bing translator
  http://hk.bing.com/translator/
  
      

Writing Guides/Tips

• The Purdue Online Writing Lab (OWL)
  http://owl.english.purdue.edu/
• University of Toronto: Advice on Academic Writing
  http://www.writing.utoronto.ca/advice
• Monash University: Language and Learning Online – Writing
  http://www.monash.edu.au/lls/llonline/writing/

• 議論文寫作 (ILC)
  http://www.ilc.cuhk.edu.hk/chinese/arguWriting/001.html
• 論文寫作 (ILC)
  http://www.ilc.cuhk.edu.hk/chinese/AWOnline/general1.html
• 學術論文寫作要領 (ILC)
  http://www.ilc.cuhk.edu.hk/chinese/AWOnline/general1.html
• 實用寫作參考資料
  http://www.edb.gov.hk/tc/curriculum-development/kla/chi-edu/resources/primary-secondary/lang/practical-writing.html
  
      

Calculator and numerical data

• Wolfram computational knowledge engine (alpha version)
  http://www.wolframalpha.com/