Hey! This plugin is pretty simple (if its possible) basically I just want other players health and mob/animals health displayed above their heads!
http://forums.bukkit.org/threads/chat-healthchat-v1-0-show-players-health-in-chat-1000.26111/ This one works in chat.
ok, but the main application here is the graphical display above the users head (thus the requirement of SPOUT)
Others have given you a few examples above the players head. If you want something a little more pretty, you could try mmoParty and mmoTarget (both Spout plugins) that add player faces and their health bar and the health of the mob or player you are attacking.