Photobucket, the popular photo sharing site, has a free Android tool that lets you edit, add effects and share photos on social networks (Facebook and Twitter) as well via email.
Snapbucket (Android Market)
You can choose from a variety of filters, effects, vignettes, and frames to apply to your photos. Filters can be combined to create your own unique filter set. New filters are added to the app as you use it more. The original photo is retained. So, you can play with your photo as much as you want without worrying about losing the original look.
The downside to Snapbucket for Android is that it is large (7MB) and cannot be moved to a SD flash storage card.
There is also a free version for the iPhone in the iTunes App Store.
Video courtesy of photobucket