The main issue with making good posters is finding the best pictures.
One of the best sites for hasbara is Israel21c.org where they have a large archive of stories that tell the good news about Israel. I contacted them to see if they have higher resolution photographs of their stories, and they responded that they often do, and which stories am I interested in?
Here's where I need your help. There are hundreds of stories at that site. If you could go through it in some random order and comment here with the URL of the stories you think would make good posters, a brief description of the story, and whether there was a good photo in the story itself, I would appreciate it!
And you won't regret spending the time at that site, either. You will learn a lot.