Themeboard is a new third-party keyboard app for iOS 8 that gives you a wide variety of themed keyboards. There are a variety of themes and theme packs to choose from, with more to be added over time.
Themeboard features work from a number of different artists in varying styles. There is one default theme, with the rest being downloadable through the app. Developer Taphive hopes to be able to update this selection regularly. There are keyboards based on themes like space, keyboards based on apps, and even a group of keyboards modeled after Apple's aluminum Mac keyboard. All keyboards feature the same autocorrect and other capabilities you'd expect from your keyboard.
You can download Themeboard for free with one default theme. Many of the available themes are free, though currently two out of the three packs for sale cost $1.99 each. Themeboard is available on the App Store now.