Ok, I see many of you having tips that work for you so I thought I would post one that works wonderfully for me.
I have to give the credit for this tip to my friend's hubby. Here's the tip: Don't throw out your old blinds ladies and gents! Take the string out and keep the plastic strips.
I am not sure how many of you have posters around your homes. I have had many issues with posters not staying up trying to use that tacky stuff or tacks or tape or nails and nothing really works. You end up with a ripped poster or it never stays up. Trim the strip to the width of the poster, tape it on the 2 shorter ends. Then drive small nails through the plastic strip and poster. It holds them up there very well.