Laying down the gauntlet to several competitors, Alien Skin software have entered the enlargement filter market with their newest Photoshop addon,
Blow Up! Allowing scaling of images up to 3600% with no stairstep, halo, or fringe artifacts, Blow Up has a rich feature list and is technologically well endowed! Considering its professional uses, its asking price of $199 isn't that bad! Go check out the
official website for more info, a demo, trial software, etc.