The fashion brand / retailer Uniqlo have teamed up with Kodansha and Shogakukan for the 50th anniversary of both Weekly Shonen Magazine and Weekly Shonen Sunday to produce a range of commemorative t-shirts.
The Japanese manga-oriented site: http://ut.uniqlo.com/sunmaga50th/
The newspaper advertised the UK site though, and on there, they're under the UT T-Shirts section, from about page 4 onwards, but there's a smaller range.
There were already some works by Shotaro Ishinomori - I can see Skullman and Cyborg 009, Osamu Tezuka - Tetsuwan Atom (Astroboy) and Black Jack, and I can also see from the new range Ashita no Joe, a few pages on. There are some others too, but I don't recognise them straight off.
EDIT 2008-04-16: I went shopping for some of the older designs:
