Does the weather have you down? Harken back to warmer months and slurp down some oysters. The only thing that tastes better is when those oysters cost $1 and you can wash them down with some happy-hour-priced drinks!
Mermaid Oyster Bar/Inn: My favorite! If you can't make it out to their nightly (5-7PM Tuesday-Friday, 4-7PM Saturday Sunday) happy hour, stop by Monday night when every hour is happy hour. In addition to $1 oysters, you can get special appetizers and great drinks for cheap. If you check in on Yelp, you can get a free side as well.
Sel Rrose: This Lower East Side bar has a great atmosphere and several varieties of oyster to choose from -- all for a $1 apiece. In my experience, it's never too crowded after work, so a fantastic option if you are downtown.
Finally, Ten Bells, where you can enjoy your $1.25 oysters with a great selections of wines and Spanish tapas. It also happens to be next door to my favorite Mexican restaurant, Barrio Chino.
For more options, check out Time Out NY's great list of happy hour oysters here.