If someone in your family is good with technology a slide show would be a thought. You could use a collection of photos beginning with their dating years and progressing up to the present. I would imagine someone must snapped a picture or two each year.
For background music you could use songs that have special meaning to them i.e. their 'special' song, music from their wedding, songs they sang to you growing up.... burn this to a disc & give copies to family members.
Don't know if you are planning a big party but you could also buy a white or light colored tablecloth & have guests sign this for a memento.