When folks ask me where they need to go in NYC, I have a short list of places I send them to. I'm not saying these are the best or anything; I just miss them.
At Gray's Papaya on W 72nd and Broadway, the Recession Special, consisting of two hot dogs (just mustard) and a papaya drink, shared with my wife, is a reliable late-afternoon snack.
Pam's Real Thai is a tiny hole in the wall on West 49th Street and 9th Avenue; I always get the red curry with chicken. After eating chicken and associated vegetables, I feel so badly about abandoning the remaining sauce that I douse the remaining rice with it or just get a spoon and eat it like a sweet and spicy soup.
The omakase (chef's choice) at Sushi of Gari on Columbus at W 78th isn't deeply concerned with being authentic and I don't much mind; the sushi is amazing fish with all sorts of interesting garnishes. I my favorites are the salmon sushi with roasted tomato and the marinated tuna with pine nuts on a tiny crisp flake of fried nori. The Upper East Side location is supposedly better (Gari himself presides) but I've found the Upper West Side spot easier to get into on short notice.
I am told that the shakes at Shake Shack in Madison Square Park are amazing, but honestly. I always get the Shack Burgers, which are transcendently good. The only hard decision is whether to get the Single Shack, which has an excellent sauce-to-meat ratio, or the Double Shack, which has more of the tasty, tasty meat. The lunchtime lines are too long to deal with; go early (11:30 am or so) or late (2:30 pm) and the lines won't be too long.
Joe's Shanghai, on Pell Street, has amazing xiao long bao - tiny dumplings filled with a bit of meat and soup. They're a bit challenging to eat and there are a variety of strategies; I prefer to poke a hole in one and let it drain into a spoon, then add a bit of gingered vinegar, and then drink the soup and finally eat the remaining dumpling. There's an location on West 56th Street, which is much more expensive but equally good. Twice a year, a famous Taiwanese chef, whose xiao long bao are even better, makes an appearance at the Sheraton in Flushing, but the scheduling is just too difficult to work out.