ZagNutz BlueCore Flying Wing:
Here's another thread on Ezone that looks interesting:
Pibros [ normally Depron but can be modified for F3 ]
F3 ( Fan Fold Foam ) FAQ:
Someone has already mentioned Genebond's BlueStick .... if you like small models its a winner.
Do a search for the Drenalyn as well. It's normally a Depron/Foamboard project but might could be modified for F3.
Hope this helps!