No recommendations, but always read the entry rules carefully. Very few are legitimate and not many of those will get you anything significant. Keep in mind that contests may not be genre specific, so you can often enter contests that are not directed specifically to your genre.
For help, check the International Thriller Writers group (I think they still do the Thriller Awards) and Thrillerfest. Your local or state writer's groups are also great sources for both contests and information about them.
Jeff