NIK have just launched an iPad application that lets you tweak photos to perfection with Tune Image or selectively adjust only a part of your photo with revolutionary Control Points. Add incredible effects with innovative filters like Drama, Vintage, and Grunge. Share photos with your friends and family with social network support, or print your photos directly in Snapseed.
I have tried it out on one of my recent snaps from Yosemite National Park and you can see the before and after versions below. There are countless options to play with and some informative instructional videos on NIKs site Snapseed
My example shot had 'drama' added and then 'grunge' which adds some textures and vignette effects, it's fun to use and innovative
Upper Yosemite Falls from Swinging Bridge (Before)
Upper Yosemite Falls from Swinging Bridge (after Snapseed)