For me, light trails are one of the most fun and rewarding styles for city photography.  It's relatively easy to set your camera up on a tripod, point it at a busy road, set a long exposure and voila - light trails.  The trick is trying to make them interesting - whether that is through finding unusual locations, mixing up the angles or doing something different in post-processing.  Here are some of my favourite light trail shots from Birmingham UK. 

Enjoy!