Whenever someone that my family knows passes away, we plant a tree in their memory instead of sending flowers and a card . The Arbor Day Foundation has two programs: one in which you plant trees in memory of someone who has died and one in which you plant trees in celebration of something special someone has experienced.
The tree saplings planted are $1 each and are one of two featured forest trees. After you choose the forest and how many trees you want planted and pay for them, you can then print out a certificate which shows for who the trees were planted, how many, in what forest, and from who the memorial was given. At each of the forests there is a registration book which lists the name of the person memorialized and where their saplings were planted in case family members want to visit one day. It is the ultimate memorial to a life to keep giving back even in death.
Here you can see the certificate of a planted tree. You can check out the program here.