German taxes:
Taxation of German rental income
Pinkernell: Excellent information on German and US taxation
Tax advisor Martin Brune: Pages of my tax office specialized on expats
German social security:
social-security: Excellent overview on contributions and refunds
Global taxes:
Expats:
Expatica: Everything for expats
Expat Access: Very good pages showing all necessary information for expats
German News:
Financial Times Deutschland (in German)