We will be driving from Grenoble to Levanto in early May. Any 'must sees' along the way or recommended stops, hotels, B&Bs or restaurants?

Thanks.

In French territory you have to choose between two directions to cross Alps: the faster is to take the A41 highway and then the A43, crossing the italian border at the Frejus tunnel; the other one is slower but more scenic and passes through the interesting town of Briançon, which worths a stop, and the Montgenevre/Monginevro pass.
The two roads gather at Oulx, val di Susa, The most valuable place to see until Turin is Sacra di S.Michele near Avigliana, a surprising 1000 years-old abbey:
http://www.sacradisanmichele.com/index.asp

Turin is a big city (1 million inhabitants) in a superb location with a lot of cultural and historic attractions. It was the first capitol city of unified Italy in from 1860 to 1866, and needs an accurate visit (1 day maybe is not even enough). If you are interested to have more information on Turin, ask for it (I know this town especially because is my father's birthplace and the seat of my favourite football team, Turin F.C.).
http://www.comune.torino.it/canaleturismo/en/

After Turin it starts the great plane (Pianura Padana) and landscapes are less interesting until you reach the Appennini area. If you take the A12, and after the Turchino pass you're going to see the sea, it means you are near Genova, another big city with interesting things to do and to see. Beware of traffic, often fouled up.
http://www.genova-turismo.it/spip.php?lang=en

From Genova to Levanto there are several fine villages along the coastline, but nothing comparable with Cinque Terre, so my suggestion is to go directly there.

Thanks Liberosette. The Michelin 'sightseeing' route takes you south through Gap to Cuneo and down to the coast at Savona. Would you recommend that route or not?

I've never experienced the Maddalena pass, but this seems to be a very steep and tortous road; probably this route is slower than the others because you're not going to drive on highways until after Cuneo.
I don't know Gap, and I don't see any place where to suggest a stop until Genova.

Thanks Liberosette.

Comments anyone?

I would not take that sightseeing route. Once you hit the coast you have a ton of tunnels. I would go via Torino then down to Genoa. Have lunch Portofino after you hit the coast.