Tacky tape. It holds the poster to the wall with a gum like substance but doesn't pull paint and paper off. It doesn't leave marks or holes either.

frame the posters and hang them like you would a picture (provided you can put nails in the wall). it looks so much classier when you do this.

If not then use those 3M sticky things or some sticky tack. These should both work well.

Use blu tack.

Double-sided tape

I have just moved house and I have loads of posters I want to have on my walls but in my new room the walls are wallpapered and I don't want to put up the posters for the wallpaper to be ripped as it is a rented house. Does anyone know a way to have posters without ripping wallpaper?