The 20th Anniversary issue of Games Master Magazine (in the UK) was a real big deal...for Sonic! It came with great free prizes (seen around on the UK pages of the site, like pins, stickers & etc) it also came inside a special slip-case (both sides seen at center, above) It features artwork from generations and around that is sonic artwork from 1991 to present. On the back of the slipcase there is info on what is inside the magazine and also there is a notice of a competition to win a holiday to the sonic themed room at alton towers resort.
The front of the magazine features some alternate generations artwork and the back features some 20th anniversary art with the tagline "Still unstoppable after 20 years". the 20th anniversary logo is in the top left. The magazine will likely be available at retail in WHsmith stores in the UK for July/Aug 2011, but can also be bought online from www.myfavoritemagazine.co.uk so anyone outside the uk can get hold of this magazine too. (quantities likely limited, buy in 2011 if you want this at all)