Darker than Black: Kuro no Keiyakusha, Kekkai Sensen Recommendations
Set in cities where a strange, other worldly gate has appeared turning the city into a place filled with the strange and wonderful. Kekkai Sensen tends to be lighter as it contains comedic elements, while Darker than Black maintains it's serious tone throughout the series.
Both series take place in a big city where some people have developped special abilities (ESP).
The main character also have powers and he works in a secret organization to protect people from bad ESP users.
The main difference between these animes is that there is more drama in Darker than Black and more comedy in Kekkai Sensen.