LEGO-touch is an application for designing LEGO creations on your iPhone or iPod Touch. From the website:
View, post, build, or edit other LEGO maniacs projects. Create your own LEGO characters in pals, post your LEGO self to represent in share. Play and download different LEGO games or challenge anyone to a build-off! Personalize your bricks with color-slider and more...
The community aspect of this software seems pretty interesting to me; collaborative designs, perhaps! - Link.
http://blog.makezine.com/archive/2008/03/design_lego_creations_on.html