Katydids. An elderly friend of mine once told me that when the katydids started up it meant that there were only six weeks left to the first frost.

Owls. Theres a screech owl down in the meadow below our house.

Coyotes. I know this is New Jersey (USA), but some nights the two bands of coyotes in our area get quite competative. Makes the dog nervous, and the cat stays in.