Newbury Street area
A few ideas. Casual:
Parrish Cafe. Good patio, pub fare, above-average sandwiches.
Coda Kitchen and Drinks. Casual but nice bar with solid American comfort fare.
Erbaluce. Northern Italian, original, great pastas, interesting wines.
Mistral. French-ish New American bistro, pretty and pricey.
Da Vinci. Upscale Campanian Italian.
L'Espalier. Creative, very pricey French/New American.
Sel de la Terre. Mid-priced country French.
Grill 23. Loud, lively luxury steakhouse.
La Voile. Authentic Provencal French.
re: MC Slim JB
As always, MC Slim JB is spot on.
I'll second a few of his: La Voile, Erbaluce, and Mistral are favorites of mine.
And I will add three:
Troquet. French-inspired new American with an excellent wine program.
Clio. Very creative, Asian-influenced new American.
Uni. Sashimi bar at Clio. New chef.
Some of these are closer than others, so map them out. Troquet and Erbaluce are a bit more of a walk, but a beautiful one. Mistral is about the same, maybe a tad further. La Voile is right down the street.
Missed the best - Bina! And a lovely walk through the common at night. Also missing is No 9 very good upscale.
I'd second on the list:
Mistral - very comfy elegant with better than average food (it's a frequent haunt for me)
L'Esplalier - very elegant, not lean against the chairs kind of place and very good
A casual place that's not readily found in the suburbs is Tapeo for Spanish tapas. Not the best in town but still good, fun and very walkable.
If you have an interest in a particular food (steaks, sushi, fish, Italian, etc), we might be able to recommend more places - you are very close to many, many restaurants all within walking distance to where you'll be.