As long as things seem appropriate and tasteful for a particular display--as small as a little corner on a table to remember a favorite pet or as extravagant as a concert fireworks or a light show for a large gathering--anything goes. The idea is to have things displayed or happening to bring a fond awareness to the memory of any thing, event or person.
At any type of memorial most often included are photographs of people, special times or places. Some might include a portrait or even a special painting. Pictures of places of interest from the past are also good ways to have the mind traveling to a wonderful time or memory. Most often these are of the person, thing or place being honored or remembered. However, they may also be of something or someplace that was special to the honoree.
Most common thoughts go to things such as flowers, ribbons or candles when thinking of decorations. These are great things to make a memorial feel a bit more special. However, other things may include a video loop played in the area, perhaps some special literature or even some personal notes. A posting wall or area can allow for others to display extra little pieces of a memory they may have relating to the rest of the treasured thoughts. Even handmade crafts can provide a personal touch. Many people remember different things in different ways and sometimes they bring out forgotten memories in others.
With a larger budget and many participants, a glorious show of fireworks high in the sky can have almost everyone looking to the heavens having beautiful thoughts and words or moans of appreciation. There are special lighting ideas and decorations that may be considered for dim indoor or nighttime sharing as well. Flashy lighting or patterns of light waving across a wall or ceiling can be very pleasing to the eye.
There is very little at times that can surpass music or song to set a specific mood. As simple as a background radio or single live acoustic performance is a great way to feel the occasion and take the mind to another time or place. Larger venues may include a full band with a stage; even a concert or many bands over the course of days will make a memorial an event to stay in the minds of all in attendance for years to come. Limits are only in the planning and the budget.