I've been embedded in Yuletide stories since yesterday, and I've emerged after my first pass with quite a few recommendations:
Fandom: Venture Brothers
Title: Cold War Christmas
If you've seen this show at all, you must read this. Truly amazing spot-on voices.
Fandom: Vorkosigan series by Lois McMaster Bujold
Title: Ingenium et Fides
I've always thought Cordelia needed more stories; she's by far my favorite character in the series, and this story fits so well into canon that it may as well have been written by LMB herself.
Fandom: Psion series by Joan Vinge
Title: Cats of Quarro
This story completely captures the feel of the books, and the character of Cat. Another story that fits almost perfectly into canon. (my only quibble is the slash pairing - in the second book, Cat is obviously squicked by homosexuality because of unfamiliarity, but it's just a quibble)
Fandom: Invader Zim
Title: One Week
One week of a journal written by Dib. Pure genius. It's like it's an unaired episode!!
Fandom: Homicide: Life on the Street
Title: Three-Part Disharmony
Yuletide always seems to come up with some amazing HLotS fic, and this one definitely fits that bill. Perfect.
Fandom: Greek Mythology
This is a really wonderful episodic look at Achilles through the eyes of others.
Fandom: Dune by Frank Herbert
Title: Knife of the Wind
I'm in the middle of re-reading "Dune", so this was perfect timing for me. I loved this so much, it's perfect. (I keep saying that ...)
Title: Tastes Like Chicken
This is really short zombie!fic, but damn, it still made me shiver.
Title: Ask Me How
The Dexter voice is really, really good in this fic. It takes the character in a new direction, and I can actually see the events happening.
Fandom: Blood Ties
Title: Sun's Light Darkest Night
Excellent plot and character voices. It makes me want to read the books oh so much, since I hear the OT3 there is more than innuendo.
Fandom: The 4400
Title: The Hurricane
I really liked this story of how the future could end up, screwed up and sad. Very well written.
And finally, the best thing I've read so far:
Fandom: Who Framed Roger Rabbit?
Title: The Merry-Go-Round Broke Down
So much meta in one story. Well-written, modern-day toons and the grandson of Eddie Valiant crack the case and save the day, incorporation of CGI and what that does to hand-drawn toons - Everyone should read this.