I found a great web service that allows to create awesome graphics online and for free. Name of this great webservice is Canva, and you can find it here.

Canva gives you everything you need to easily turn ideas into stunning designs. Create designs for Web or print: blog graphics, presentations, Facebook covers, flyers, posters, invitations and so much more.

Canva offers a lot of already predefined designs:

Facebook header template

A quick modification, and we can customize templates as we wish.

Canva offers templates for most various life situations, templates for Google+, Facebook, Social posts, presentations and more.

Yesterday I played with Canvas and created some graphics:

Header image for Terramatris Facebook page

Another neat feature of Canva - it allows to collaborate many designers together:

Canva makes it easy to work with others, letting you share and edit your designs with family, friends and coworkers.
Professional designers can easily collaborate with clients. Never worry about frustrating back and forth emails again. Canva also plays nice with traditional desktop design software

To signup for Canva it's enough to have a Facebook login, but you can signup using your e-mail as well. 

Canva is free for use, they might charge you some small money if you will use some PRO images they offer.

Visit Canva and signup to learn more.