Google it - there is a fair amount of information out there. It is sometimes called the AFE Zone. The technical term is Anterior (front) Fornix (juncture) Erogenous Zone. This is where the cervix and vagina meet just behind the abdominal wall.
There is also another spot 180 degrees away called the PFE Zone. It's the Posterior Fornix.
My wife likes both stimulated (at different times). The easiest way for her to achieve an a-spot orgasm (which is always very wet) is to be on top. She grinds her clit into my pelvic bone while the head of my erection impacts her AFE Zone.
On the toy side - larger slightly curved dildos and vibes like the G4 Big Boss and Vixskin Maverick do a terrific job of hitting the spot and can easily be turned around to hit the PFE as well.