Not much really. They're gonna spend a lot of time chasing people off the verges. English Heritage really are grabbing f*ckwits. You could park in Amesbury and walk down the old Stonehenge Rd, which eventually joins the A303. Great view of the Stones from the ridge.
Of course, when the road is taken up and the tunnel completed, you're not really gonna be able to see Stonehenge from anywhere nearby for free. You're gonna have to pay to get into the Hengeworld theme park to get anywhere near the stones.