Sirius (or Padfoot as the case might be)/Harry:

Title: Just One More Secret or at AO3 by marguerite_26
Rating: NC 17
Pairing: Sirius/Harry
Word Count: 4000 Approx.
Summary: A dog can be a lonely young boy’s best friend.
Warning(s): sentient bestiality, underage sex, knotting, age difference
Notes: Have you not read this fic?? It's so naughty and delicious. It's Sirius in his animagus from. With Harry. Doing things. It's HOT. Okay? So hot.

Title: Wild Men by traintracks
Rating: NC 17
Pairing: Sirius/Harry
Word Count: 2,380
Summary: Harry watches Sirius strip off his putrid rags by the side of the clear pool. "God..." Sirius sighs, scratching his chest, turning his bare white arse to Harry. But not before Harry gets an eyeful of the other.
Warning(s): cross-gen, underage sex, age difference
Notes: Placed in Third Year, while Sirius is hiding in the cave and Harry goes to visit him. Hot, so very hot (there's water!sex!) but gentle at the same time because both Sirius and Harry are so starved for love.

Harry/Teddy:

Title: 90 Seconds by traintracks
Rating: NC 17
Pairing: Harry/Teddy
Word Count: 1,820
Summary: It's Harry's birthday, and Teddy has teased him one too many times.
Warning(s): cross-gen
Notes: So, so sexy, this story. With in charge!Harry, who is going to teach Teddy a lesson about temptation. And he is such a tease here, but hey, you won't hear Harry complaining. We all win.

And a bonus. A pairing which I have read very little. But this was fun. Harry/Snape:

Title: What a Wanker! By Jordan Grant
Rating: NC 17
Pairing: Harry/Snape
Word Count: 400
Summary: Harry gets more than he bargained for when Snape asks him to stay after class.
Warning(s): cross-gen
Notes: This is Drabble, in which Harry learns not to call Snape a wanker. Ohh, the lulz. It's awesome. :D