I couldn't just pick one fic, so I picked two - here's one.
(I'm procrastinating, I should be reading medieval manuscripts.)
Story: Finger on the Trigger
Word Count: 2,546
Author's Summary: Eleven has an inner gun-kink he isn't aware of yet. River fully takes advantage of this.
Characters/Pairings: River Song, The Doctor (11th)
Warnings: Explicit Sex
Recced because: This is not only very good smut (I appreciate good, original smut), but also well-written. The Doctor and River are very much in character and, more importantly, their timey-wimey not-in-syncness plays an important part in the story, too, which not only fits with canon very well, but also keeps the reader on his/her toes.
The dialogue is quick and witty (see preview) and really adds to the action that takes place. As much as this is a smutty oneshot, I do like it when there is a bit of framework involved - this isn't just River and the Doctor doing nasty things, there's a fair bit of psychology involved. After all, River knows something the Doctor doesn't (always a good place to start) and gently pushes him into knowing himself just that little bit better (through sex) and we get to see it.
River has the upper hand in the story and it is really interesting to see the way the Doctor responds to the things she does (I personally especially like the babbling - 'Nervous? Of course I'm not nervous! Not at all. I'm a Time Lord, I walk in eternity. Do I look like I'm nervous? No! Don't answer that!'). The 'power' dynamic in their relationship in canon is fascinating to begin with and this is developed in this fic very well, too. It could totally have happened at some point.
Well, and I may have a bit of a thing for dirty talking - and River does that very well.
River, I've been chained up and threatened by ... well, by amateurs, actually, but it still wasn't much fun ... and now I'd really like —'
'Some fun?' River arches an eyebrow. 'That can be arranged.'
'Fun? With me like this?' She lets him think through what he's just said. 'Oh. Oh! So what sort of fun would that be, then?'
He's intrigued. That's good. 'Well, right now, Doctor, you're actually my prisoner, so I can do what I want with you. Is that starting to sound like fun to you?'
'Um. Maybe? I don't know. It's the handcuffs, isn't it? You have a thing about them.'