EliteWarn is my second plugin on BukkitDev, it features a config this time ;) It allows you to warn players and if they get to a high enough warning level, they will be unable to join. You can customize most of the settings too. It is in it's first release so it may have a few glitches. All you need to do is type /warn <playername> and it will add them to the configuration. You can manually edit the warns.yml or you can use /clearwarnings <playername> This won't remove them from the configuration though, so it might be a good idea to clean it out every once and a while.
If you warn a player that is not online, it will display that you warned a offline player, this lets you warn any username. This plugin was not designed as a replacement for any banning plugin. If this plugin happens to crash or have a error in the config. It WILL let any player that has max warning level join the server! Always test by warning yourself a couple of times before you start using it fully on the server. I am not responsible for any griefing done to your server if this plugin fails to load or lets a max warned player join the server. Thanks and have a good day.
None that I've found.