CreeperMemorial is a simple bukkit plugin that causes creepers to leave a memorial when they explode.
After installing this plugin, whenever a creeper explodes it will hurt nearby players and mobs (as normal), but it will not destroy the environment. Instead the 'splody creeper will leave behind a two block tall memorial pillar made of the material the creeper was standing on. If the memorial is grass blocks, a flower or rose grows on top of it. If it was is stone, cobble, or gravel (and it is dark), a red or brown mushroom grows on top of it. If it is dark, a torch will appear on top of it.
There are no configuration files for this plugin, so after building, simply add CreeperMemorial.jar to your bukkit plugins directory and restart your server.