BigBlk is right. You need to manual focus for night sceneries. You can spin your lens to 'infinity' in many cases since the closes focal point is beyond the longest focus reach of the lens anyway.
For weddings I use a flash, even though I have very fast glass and high end camera with high ISO because, frankly, a properly used flash picture looks really nice. I went from a shoe mount (in the hot shoe on top of my camera) to a bracket with a PC cable, and now use Cactus triggers and handhold the flash. Works great.
When I do night scenery shots like the ones attached, I use a good tripod, close the aperture as far as I can (read large aperture number), turn down the ISO as low as it will go, manual focus (or set for infinity), and use a wireless shutter trigger (you can use a cable release for older cameras) so that I don't touch the camera to trigger the shutter. I also add a neutral density 4 filter and a polarizer which further reduces the amount of light coming in to the lens so I can leave the shutter open longer. This makes blinking light sources appear as solid light, and also smoothes water, clouds, and makes head and tailights on cars look like streaks. Very cool.