Canva is a new poster design tool which is currently in beta.

It allows for the creation of posters by dragging in images and text. A range of free images are available, or a wider selection can be used for a payment. I'm not sure how many people might pay for a particular image or just use an alternative tool, but the interface and look is quite nice, and it's easy to generate a good result quite quickly, which looks attractive.
A range of formats is also available, for creating posters, Facebook headers and other documents.
Here's a social media card that I created, showing my Twitter name for those of you who don't already know it.
Worth checking out.