Ralan.com is an excellent site for finding sci-fi, horror, and fantasy publishing opportunities. According to the description on the homepage
It provides up-to-date listings of markets in the speculative and/or humor genres only. It started in 1996 as a way to find markets for my work, organize writing links, and share this information with other writers. Soon other writers started helping me back, pointing out new markets and noting changes in listed ones. This two-way interaction continues today. There are now other sites that provide literary markets and links, but thanks to many of you, Ralan.com is still the most up-to-date in its field.