Our band hall has a bulletin board inside each side of the building that has an entrance. Which is two.
Because of where they are and who usually uses those entrances that is how we use ours.
One being where the students enter we use that bulletin board to post fundraiser deadlines, upcoming events, photos, anything of interest for the students.
The other entrance is where parents enter and we use it for our "2 Hour Power Pledge Fullfillment" and place paw prints with all the parent names that have fullfilled their 2 Hour Power Pledge each year. Before meetings I see parents there looking at the names and talking about who's who.
So probably the most effective ideas for bulletin boards depends on where it is as to how you use them.