I searched for a re-post and didn't see anything...
So, if you kill the second boss in SFK and all of his spirits, He gives ~18% daily guild xp with a 5 player guild group on heroic.
I haven't tried doing this without killing the spirits, but when you do kill the spirits then the boss you get almost 50k per spirit, meaning 50k 4 times, per person.
I guess this doesn't technically count as an exploit, but I'm sure it's not intended to give 18% xp for 1 kill. Still really helpful for when you look at your guild xp at 10 PM and realize you're only at 50%.
P.S.
I haven't tried to kill him without killing his adds so I don't know if you still get a bunch of guild xp without killing them.