The official IBNS-Homepage (International Bank Note Society) is always worth a visit. You'll find a lot of useful information concerning 'Collecting of Banknotes'.
Banknotesworld.com - The ultimate banknotes forum for the German speaking region with an incredible gallery ... a must for every interested banknote collector.
Moneypedia - The German online lexicon about banknotes including biographies, geographical information, signature charts and many many more.
   
www.banknote.ws - The cumulative collection of Ronny and Captain Peter contains a lot of rare banknotes and provides interesting and details information together with scans of the respective banknote.
The homepage of Ron Wise (US) as of today probably offers the highest number on banknote scans in the net. It's always worth a visit.
Johann Kodnar offers information on Austrian paper money on his homepage. Among others it contains a gallery with scan of Austrian notes (banknotes and Notgeld) from the 18th century up to today, a brief history of paper money and a inventory of collectors and dealers.