It depends on the food you want, and the price you're ok with paying, and where you're staying (I live in NYC so can probably give some pointers on what to avoid and where to go)
French, Spanish and Latin American cuisine are very big here; French is usually seen as v high end and a lot of the michelin restaurants (or the ones that aspire to) are these so expect OTT obsequious service. Spanish is also big as it's seen as European so having kudos; then there's lots of Latin American places which are fantastic - Peruvian cuisine especially. You will pay big $$$ for excellent places, and all bills will come with sales tax, plus expect to add on a 20% tip. Anything less and they'll know you're from the UK / mainland Europe
Generally try and steer clear of anywhere round times square as it's all pretty generic and rubbish (like leicester square in London)
Out of all the places suggested so far, I'd recommend The River cafe. Its at the top end of brooklyn right by DUMBO and is on a converted barge so if you can snag a table by the windows you can see the lights of Manhattan. Went there for my birthday last week and it is excellent; however if you're taking a bloke, they'll need a jacket (of the collared variety)
if you want authentic NYC steak house, then go to Peter Luger's in Brooklyn. It's been there for decades, comes well recommended and blokes usually love it as you can get half a cow
not particularly near a subway station but not far across the river so a cab is cheap and easy peterluger.com/
I'd avoid Les Halles if you want a unique experience; the food is ok but nothing special, and it reminds me of a cross between a cafe rouge and something similar (I was going to say a French brasserie which is daft as that's what it's modelled on!)
I can recommend some more if I think a bit longer; I'd also suggest making a visit to Katz deli on the lower east side for typical NY deli fare (1lb pastrami sandwich) and doing something for brunch on Saturday or Sunday as it's a very NY thing to do. Lots of places do bottomless brunch deals so you can get quite squiffy for quite cheap!