A monopod could be helpful, but I think more for long zoom shots, or slightly lower light or slower shutter shots. For full-blown nightshots, with shutters over 1/2 second, there really isn't a substitute for a tripod or at least a level surface to place the camera on - best to be as hands-off as possible!
With a good DSLR or higher-end prosumer, the high ISOs can help you get by for some nighttime snaps. And a monopod can help you push the shutter down to nearly 1 second in speed for when you need to pull in more light. A tripod will ultimately be best for night photography where you can leave the shutter open for many seconds and pull in the lush, saturated colors and lights and textures. Consider getting a small, portable tripod, or table-top style tripod, for when you don't want to lug around your full-size one. I have an old Vivitar tripod that when folded is 10" long and can fit in my camera bag, but can still extend to 48" when open - it is less stable than a full-size and won't support any mega-lenses, but works just fine for a standard camera body and is very convenient to bring along. If I don't feel like carrying the big tripod, I just slip the compact one in the overflap of my bag, where I have it if I need it.