If you are trying to do night/dark w/o flash you will need a fast lens. The lower the f/stop the faster(1.8 is faster than f/4) The IS will help but I'll take a 2.8 zoom over an f/4 with IS. That's just me. The IS will help for longer shutter times, however, if you are shooting people and need to freeze the action to get a sharp picture you will need 1/60 or faster shutter speeds. To get that in dark situations you need a faster lens. If you want to spend around $1000 get the Canon 24-70 2.8 L. It is a very usable range and it is a constant 2.8. If you are not ttrying to spend a whole bunch of money, I second the motion that you should pick up the 50mm 1.8. It is a must have. I have the 50 1.4 version, a little bit faster for $350. Using a 50mm will also help you with compostion, because you will be using your feet as the "zoom". Plus the 50 1.8 has very nice bokah and it delivers the most bang for the buck IMHO.