Many servers have a showcase mod that allows items to be suspended permanently on a block, but something along the lines of that is coming to vanilla. This screenshot was included in a tweet by Nathan Adams with the caption, "Gentlemen, prepare yourselves and choose your weapon... for tonight, we go to war." Nathan has replied to many questions on Twitter about this new feature, revealing that the 'frames' as shown above will be able to hold any item or block in the game. If you don't like the transparent background, don't worry because Jeb is putting in some nice ones (picture). Minecraft 1.4 is going to be awesome!
Source: @Dinnerbone