The Panverse novella-anthology series is looking to publish volume 4, with a scheduled publication date of September 1, 2012. To this end they are reading for submissions with no hard close date, until the anthology is filled. They're looking for:
Pro-level novellas of between 17,500 and 40,000 words. We are particularly interested in core SF stories, as well as Fantasy and Alternate History. With Fantasy, note that we gravitate toward urban and edgy, though we do have a weakness for non-sappy stories involving Faërie or Sidhe characters.
Depth of characterization will count for a lot—however clever the idea, if we don't care for the protagonist, we'll reject it. We like stories that instill wonder. Give us a character we care for, a world both interesting and well-developed, and a story that carries us along, and you've probably got a sale.
There is also a detailed list of what they definitely don't want, including military SF and vampire stories.
Pay isn't great, at around $75, however they say 'The Panverse series is the premier anthology for all-original SF/F novellas in the market today' and there is at least a guarantee of industry scrutiny, which counts for quite a bit.
You can find the detailed submission guidelines here: http://panversepublishing.com/subs