Our coding department released this piece of art recently:
TekProtect: Modded Minecraft Bukkit Server Protection
TekProtect works silently in the background, under the thread name "CheatBlocker" and helps eliminate Hacked Client users in Modded Minecraft SMP Servers. It renders mods like x-ray, Fly hack, Kill Aura, No Weather, etc... unusable, all passivly. Preventing a user from hacking prevents admins from issuing bans, and having to deal with awkward situations.
Plugin works with 1.4.5+