2003 Archive 
Well that was a long wait. Almost 40 years after the last TV 21 annual was published in 1972, this summer will see the publication of "Gerry Anderson's Century 21 Annual 2011". As you might imagine, details are few right now, except it has 96 pages and will be published by Reynolds and Hearn on August 31 2010. Not September 13th as some might have hoped.
It is listed as a hardcover and the cover art looks really nice, as you can see. It's available for pre-order from Amazon.co.uk.
In addition, Reynolds and Hearn has published 2 additional volumes to the "Century 21" series of books featuring the classic strips from the comic. There are now 4 volumes in total, available in paperback and hardback, although the earlier volumes are now getting spendy in hardcover format. They are excellent books and well worth picking up.