Buying a board can be a confusing process. Lets go through a few things before we get to the selection of a board. First you have to know what kind of board do you want. Are you a freestyler or a freerider? Maybe you want both.
After you figure out what kind of rider you are or want to be, then the next step is to figure out what the measurements of your new board will be.
Frostyrider has a great size/width calculator and even gives you suggestions on boards.
There are many other aspects to boards to choose upon. Some are softer and some are stiffer. As a beginner you should go with one softer as it will help you in turns. Stiffer boards are better for higher speeds.
If you have big feet, you should look into wide boards. Recommended if you have feet sized 10-11 and basically required for people with sizes 12+. I have size 10 boots and i barely fit my regular sized board.
Also if you are on a budget, try to find a board during the offseason, and also from craigslist if you don’t mind a used board for cheap.
NYC locals: check www.paragonsports.com for a local check on inventory. (also for deals)