MemeKeeb
MemeKeeb is an iOS app & iMessage extension to help you quickly and easily transform text and make memes.
There are a number of text transformers which will convert your message into a variety of different formats, like the "sPoNgEbOb sArCaSm MeMe TeXt", upper or lower case, as well as a handful of others. There is also a Meme Maker, which provides popular templates for creating memes. Just select an image, add your text, and send!
There is also a dedicated iMessage app, so you can make a meme and share it with your friends all from within Messages.