The stock cooler is all you "need." It's made to prevent the CPU from overheating under stock configurations.
But it's loud and, even though you're CPU will operate at acceptable temperatures (by Intel's standards), it can still get pretty warm.
So why do people get aftermarket coolers? Well, they are coolER and quietER than you NEED for stock operation. If you want a quiet PC, get a big cooler with slow fans. That will also keep things cooler. The bigger the cooler, the more heat it can pull from the CPU, and that leaves less work for the fans to do, which means they can be quieter because you can lower the fan speeds.
If you want to just run stock for now, or want to just put money elsewhere, just get an aftermarket cooler later. The best air cooler out right now (if you can fit it) is the Noctua dH15:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835608045
Noctua also makes some of the best fans because they are quiet and move enough air. Other fan companies make good fans too, but you can't go wrong with Noctua 120mm or 140mm fans (in black or brown) unless you get the 3,000 rpm version (they are too fast and, accordingly, too loud).
For an all in one (AIO) water cooler, I'd recommend not using the fans they come with unless you know they are good. Usually, AIO's stock fans are super fast and super loud unless you mess around with them, and that's annoying. So if you can, factor in the cost of the AIO + the Noctuas (or good fan of your choice).
No AIO water cooler will keep temperatures
significantly lower than the Noctua dH15 air cooler, but they can look nicer. The dH15 will cover your whole motherboard. AIOs won't block your view as much because you only see tubes. This matters only if you have a case window, or otherwise leave your computer parts exposed.
Hopefully that helps. Good luck!