first up- PicMonkey. This is by far the greatest tool I use, and if you don't have an account with them yet, then you need to go sign up, like right now. One, the site is free. You can pay a pretty reasonable fee ($33 for a year) to become a "Royal" member , which gives additional fonts, pictures yadayada-totally worth it. The site allows you to edit, create, touch-up and do just about whatever you want to your pictures. Lose a few pounds, add some pizazz, use it to make your pictures all the same size. PicMonkey = the best!
Besides picmonkey- I like to use...
ABM (A Beautiful Mess)- this one is great for making collages on your phone and adding some color, not much editing though
PicTapGo- this is one of the best for light editing, you can take a dark picture to a beautiful well lit photo with just a click
Repix- this is a new one for me, I haven't used it much but it's kind of a mixture between PicTapGo and Instagram.
and that's just about it...what types of apps do you like to use for editing?