Photogene, Photoforge2, or Snapseed?
I use them both, they are compatible. For down and dirty I use Snapseed. For a bit more involved editing I use Photogene as well as Photoshop Touch . Sometimes I run the same image through both. The result is better than the result from either alone.
I should state that I NEVER use the canned effects in any of these aps. I use them as if they were all CS5 for straight photo editing.