Some of these I've shared before, but thought it would be useful to have them in one place.
1) Nobel Prize Winners - Posters explaining Nobel Prize-winning ideas. The writing is quite small so these would need to be printed in at least A3. Thanks to Ali Mclean for putting me on to this.
2) Economic and British Values, Economics Careers and Why Study Economics? posters from Tutor2U. These are free to download and print yourself, but the latter two are also available to buy professionally printed. I believe there are more posters from Tutor2U on the way. (Update: they've added a set of posters highlighting female economists)
3) Choose Economics - I've shared these before, but I made them with the aim of showing that Econ is about more than just money.
4) Economist Covers 1997- present and pre-2003- I haven't sorted my displays out yet (!) but I'm tempted to pick covers from key events in UK and Global economic history. There is also this collection which traces views on inflation over the last 50 years.
5) Stange and Unusual Taxes - some of the more unusual taxes across (largely US) history, and also has some interesting images that would make nice posters.
6) Infographics from Atlanta Fed - some are probably too US-Specific to be useful, but others would work well.
7) Classroom Display from Economics Factory - including study skills
There are also some ideas on displays more generally in this old post.