While Adobe Photoshop Express takes the cake for most practical app I found, Lo-Mob is the most fun. Based largely on vintage and unusual photographic tools and techniques, Lo-Mob gives you 41 filters to apply to photos you’ve already taken or photos you take in the app (though the preview of the image does not show the filter effects and you can swap between filters after taking the shot). Once an image is selected, you are taken to a screen that lists all of the filters with a thumbnail version of the filter as applied to your specific image–a nice way to get a quick idea as to which filter to use. There are also adjustments to be made within each filter, which lets you have some control over the image without having to do the work of creating an effect from scratch.
This app is what I wanted from Hipstamatic and I anticipate using it for most of my photo effects.