iPad Apps
Phoster
Let's you create professional looking posters with ease that can be printed at a variety of print grade options.
Pages
Pages is Apple's word processing App that comes with your devices. It's very flexible and powerful. Is just depends on you having ideas for yourself.
Canva
This awesome free App is also a website which can be accessed with the same Account. It's an excellent tool for you to make your own Posters - as well as many other formats. Very professional, modern and hip templates to fire your imagination. Very easy to edit everything on your page.
Web Tools
Posterini
So many different types of poster templates here there is sure to be one that inspires you. Quick and simple to use.
Poster my Wall
Loads of templates allow you to make excellent posters.
Piktochart
Also an iPad App, this app allows you to make very professional looking icon based charts. Great to sharing information in a clear and concise manner.