I'd rather you learn why you are to use a resistor of that resistance rather than just tell you which resistor to get.
Visit the LED wizard page and enter values to see different resistor values. Most LEDs you're going to be using will have a forward voltage drop of 2v, and a forward current of 20ma. And for the source current it depends on how many batteries you will be using. 1xAA = 1.5v, 2xAA= 3v, 3xAA = 4.5v, 4xAA = 6v, etc. So by entering 6, 2, 20..You will see it will recommend a 1/4watt 5% 220ohm resistor (even gives you the color codes!). Now where does 330 and 340 come from? That is just people being over protective of their Light emitting diodes!! It is current that drives the LED, and resistors limit current. So if you give it less current it will be dimmer but will last longer. Visibly though, you won't be able to see the difference if you use 220, 330, 340, etc. You may however see a difference if you use no resistor (which will blow the LED in a few seconds), or a 1K resistor which will be pretty dim.
If you ever build a circuit with LEDs powered by 2xAA (3v) as 3.3v tolerant components are common in electronics, you will be using LED resistors in the area of 47, 51, or 56 ohms.http://led.linear1.org/1led.wiz