According to Verisign there has been a 402% increase in sales of chinees ccTLD this year and the .CN is now the 5th most popular ccTLD domain ending in the world (See Nick post at Multiligual).
.DE seams to be the most popular and number two to .COM (gTLD), but .CO.UK seams to have most pages indexed in Google.
Brother to .COM is the .BIZ gTLD, Neustar reports that they have 1.7 million endings registered, which puts it number 10 on the popularity list.
ccTLD = Country Code Top Level Domain.
gTLD = Generic Top Level Domain