The deadline for the Black Orchid Novella Award is May 31. They are looking for original novellas of 15,000 to 20,000 words that are written in much the same vein as Rex Stout's Nero Wolfe stories. You can find all the submission details here
This is one of the most prestigious short story contests in the mystery genre. There's no entry fee and the winning entry is published in the Alfred Hitchcock Mystery Magazine.