Useful resources:

Government departments and agencies:

Europe:

• European Patent Office
• European Patent Office - esp@cenet
• Office for Harmonization in the Internal Market, Trade Marks and Designs
• Austrian Trademark and Patent Office (In English and German language)

North and South America:

• United States Patent and Trademark Office
• US Patents Search by Google
• Tools to get US patents on PDF format
  
• National Institue of Industrail Property (INPI) of Brazil

Asia

• State Intellectual Property Office of the People's Republic of China
• Trademark Office, State Administration For Industry And Commerce of the People's Republic of China
• The National Copyright Administration of People's Republic of China
• China Intellectual Property Net
  
• The Customers General Administration, People's Republic of China
• Intellectual Property Department, The Government of the Hong Kong Special Administrative Region
• Search for filed and granted patent in China (Chinese site)
  

Australia

• IP Australia
  

Africa

• Companies and Intellectual Property Commission, South Africa
  

Others

• World Intellectual Property Organization
• Directory of Intellectual Property Offices