I ran across the new market Blaster Books over at Ralan.com this morning. They're looking for science fiction stories in all the sub-genres including mystery. Shorts of 1000 to 5000 words will be published on their blog and payment is $50. They're also looking for novelettes of 7500 to 17,499 and novellas of 17,500 to 39,999. The advance for novelettes is $100 to $250 and for novellas $300 to $950 plus a 50% royalty split. You can find the details here.
Now, while this is a paying market you'll find that there are many grammar and spelling mistakes on the site so submit with that caution in mind.