I currently have:
Camerabag: One of the first apps I bought, great for filters!
Quad camera: A Lomo Actionsampler effect camera, more gimmicky than useful...
SnapFilters: Quirky little app, can change the vignette, colour, have a square format photo, and so on....plus it's FREE.
Mill Colour: Free 'Looks' photo app, very good, I use this all the time.
Panorama: Expensive but well worth the money great for creating panoramic photos, either portrait or landscape.
Mobile Fotos: Flickr Uploader and viewer, great interface.
Colorsplash: Great app, a must buy.
Polarize: Free app, for the 'Polaroid' look
Vintage Series: Red, Black etc.
Photobox: Free app from the makers of polarize, another 'looks' app, but in it's early stages, I've had issues with resolution hopefully will be sorted in the next update.
I have others but, but too many to mention, hope this helps all
