Besides the ones above that I commented on, here are some other that I like:
Montalcino:
Boccon Divino is one of my all-time favorites in Tuscany. The family that runs it, is just so super kind and amazing. The food is to die for! The wine list is very extensive with some nice older vintages. And if that wasn't enough, the view is heavenly. They often serve a free "welcome" dish of pappa al pomodoro. Despite how simple of a dish this is, it truly shows you what you are in store for, for the food to come. Try the liver pate, the cartamusica dish, if available the gnocchi with truffles (melts in your mouth!), l'antico peposo made with Brunello!, plus many other amazing dishes!!!
Osticcio is my back up place in Montalcino to take clients to on the days when Boccon Divino is closed. Much simpler place and menu. Food is still outstanding though. It is technically an enoteca, so wine is their primary focus. This means that their wine list is beyond extensive. Make sure to reserve a table by the windows!
La Taverna di Baietto this is a simple place with decent food. The real reason to eat here is that it has the same owners as the wine bar/shop across the street - Enoteca di Piazza. So while this tavern has a good wine list, you may also get flights of wine from any of the 100 bottles they have on their enomatic system across the street in the shop. Have you been wanting to try that 130 euro bottle of wine but don't want to drop that kind of money? Try a flight instead for 9!
Bagno Vignoni:
Osteria del Leone is a very small, intimate restaurant with great food/wine in one of the smallest and most intimate towns in all of Tuscany!
I could go on and on, but unfortunately, I need to get going.