The other bus (the rate will be going up sometime soon to $2). If Wall Street is the destination, then I'd take the bus below to 74th, then the #7 train to Grand Central, then the #4 or #5 to Wall St. If you get a metro card the transfer from Bus to Subway if free, if not then it's two fares, the one subway to subway will be free. It's not a fun trip from Laguardia into the city by public transportation.

You can also take the Q33 bus to Roosevelt Avenue-Jackson Heights or 74th Street and Broadway in Jackson Heights Queens. If you get off the bus at Roosevelt Avenue, you can catch the E or F trains into Manhattan. If you get off the bus at 74th Street, you can catch the #7 train heading into Manhattan. This train stops at Times Square where you can transfer for free to another train to take you anywhere in the city. For a detailed subway map, visit the MTA's page.