A few ways to get to NYC from Secaucus.
As previously mentioned, the bus in front of the Embassy Suites, that will take you to the main bus station about a block from Time Square. You could kill a day in that part of town easy. Theatre, stores, food, it's all there.
You can take the bus to Hobokin or Wehawkin (NJ) and take the ferry over. Last time I did it, it was $2 or so. Or you can do the limo. Expensive, IMO, but for private, comfortable transportation, it's the only way to travel and avoid public transit.
Cab ride to lower Manhattan, last time I did it, was expensive. Take the subway or if it's a nice day, it's about an hour walk. Not much down there besides business district, but if you're interested in seeing Wall Street and such, it's worth it. Of course, right around the corner is the former WTC area.
If you get that far south, definitely hit Canal Street for bargain knock-offs (jewelry, sunglasses, electronics...not murder...more on that in a bit). Breitling, Rolex, etc for under $30. I bought a Breitling knock-off several years ago and it still works like a champ. One prick back at school chastised me for buying a piece of crap, yet I still fool Breitling dealers with it.
Last time I walked down there we came across a double homicide that happened within the last 15 minutes. At first I thought the cops were being total pricks they way they treated passer-bys, but then I watched some of those folks and thought the cops were showing great restraint not knocking the crap out of some of them.
2000Flyer