20110627 Now that is inflation!
There was a period of hyperinflation in Germany (the Weimar Republic) between 1921 and 1923. This is one example of a number of German stamps, from that period, with a surcharge applied, I had collected in my more youthful days (1950's). It is enlarged here to show detail, but it is just an ordinary size stamp, despite the price :-).
"A surcharge is an overprint that alters or confirms the face value of the stamp. These are commonly used when stamps to the required denomination are unavailable, perhaps because new shipments have been delayed, or because circumstances have changed too quickly to produce an appropriate new issue. The approach has also been used to use up existing surplus stamp stocks. It can also change the usage of a stamp, for example from surface mail to airmail, or from postage paid to postage due.
A famous example of surcharging was during the German hyperinflation of 1921-1923. Stamps in the 10-20 pfennig range were no longer useful for paying postage, since hundreds would have been required on a normal letter. At first the government overprinted existing stamps with values up to 10 marks while it was producing new ones, but by 1923 even the newly printed stamps up to 75,000 marks became useless. These were surcharged with even higher values, up to 2,000,000 marks and then a round with values up to 10,000,000,000 marks (10 billion) before the financial system was reorganised to address the hyperinflation". en.wikipedia.org/wiki/Overprint
Also shown in "Seeking Alpha":