There are plenty of science fiction magazines (online and/or print) that you have yet to discover. I had wanted to list all of the magazines I'm familiar with, but I found a list online that was much greater than mine. So I'll mention the website, instead.
Although many writers may not want to share this treasure trove for fear that with more competition, they would have less of a chance publishing in those magazines, I believe competition is good for the writing community for two reasons:
1. If more people know about the magazine and submit stories, the selection would be better, and, therefore, the magazine would be more enjoyed by its readers.
2. With more competition and better stories, the writer would have to improve his/her craft and, therefore, write outstanding stories.
The list comes from www.everywritersresource.com. You may find that some of the magazines no longer exist, but the list is extensive even without them.
A list of science fiction magazines: http://www.everywritersresource.com/sciencefictionmagazines.html.
Also, below is where you can find a top ten list of science fiction magazines from the same website. Some of the magazines are not in the longer list, so be sure to check them out.
A list of the top ten science fiction magazines: http://www.everywritersresource.com/topsciencefictionmagazines.html.
Whether you are a writer or just a reader, I hope you enjoy. Are there other science fiction magazine websites that you want to share?