Well I am using a neck made of exotic wood SEE PIC (don't really know the name, I think is Bangakiray....or something like it....the guy ho sold it to me told the name, but really not too sure), laminated with mohogany thin strips. I made a 4 string bass neck with the same wood, and it's quite sturdy, I had to slighly tighten the rod 2 time in 4 months, but no big bowing anyhow.
I am planning a ultra thin neck, like my Ibanez S ( Frank Gambale model ), probably the thinnest neck I ever played with, that will be fun to make !
Rob