Domaine des Ardoisières is probably my favorite address for Savoie whites, and certainly deserves a mention here, though I can’t claim to be a true expert on the region.
Belluard is a recent discovery, I was impressed by the purity and transparency of a bottle of their varietal Grignet (the Les Alpes) last week (does anyone know of any other producer offering (a) mono-cépage Grignet bottling(s)?).
+1 for Ardoisieres, although I like the Argile Rouge as well.
I’ve understood that outside of Belluard’s vineyards Gringet is pretty much non-existent.
For Altesse (aka Rousette du Bugey, Rousette de Savoie), I like Peillot, Dupasquier, and Belluard. Belluard’s Gringets have also been mentioned here and can be pretty special. Dupasquier and Peillot make pretty decent Mondeuse as well. My favorite wine from Savoie is the Renardat-Fache Bugey-Cerdon, that pink off-dry sparkling elixir of liquid happiness.