Cocktails and dinner in backbay / fens
One of my favorite cocktail/dinner combinations is the bar at Eastern Standard in Kenmore Square for drinks, followed by a ten-minute walk to Trattoria Toscana in the Fenway for dinner. The former is one of the few places in town where they take cocktail craft seriously, the latter is a modest hole-in-the-wall with awesome Tuscan cuisine (though they go farther afield on pastas).
If money is no object, the rather overpriced Sorellina in the Back Bay might do the job: good drinks, cool atmosphere, slightly creative luxury Italian, a generous dose of hotspot buzz.
Clio is another good pick if you don't care about a massive tab (its bartending could be stronger). Its downstairs sashimi bar, Uni, is also pretty amazing, and breathtakingly costly.
If elaborately-plated luxury New French built around local ingredients is your fancy, I'd suggest L'Espalier, another Back Bay place where it's hard not to drop $200 a head. Cocktails are decent, not extraordinary: they're all about their jaw-dropping wine list.
The cocktails at Douzo in the Back Bay are decent, plus they have some interesting sakes, and it's a handsome, fun, broad-menued Japanese place with lovely if not incredibly exotic sushi.
No. 9 Park has the other stupendous bar on this side of the river (it trained a lot of Eastern Standard's barstaff), though it's technically on Beacon Hill. I'm not so enamored of the dining room fare -- I think it's a little pricey for what it is -- but just having a drink there and finding dinner somewhere else is worthwhile. Another two-fer I like is drinks at No. 9's bar, then dinner at nearby Grotto, another budget-priced Italian in a cool, funky Beacon Hill basement.