Put That Back Where It Came From (or so help me) (http://vorpalblades.livejournal.com/167625.html) by vorpalblades (CWRPS/Monsters Inc, Jared Padalecki/Jensen Ackles)
- this is an incredibly adorable piece, and Boo, Mike and Sully's cameos are fabulous. It's a very sweet boy-meets-boy-dressed-as-a-monster fic, and Jared and Jensen really shine in it.

Thirtynatural 'verse (http://pixienotes.livejournal.com/tag/thirtynatural) by pixienotes (30 Rock/CWRPS, gen with overtones of Jared Padalecki/Jensen Ackles)
- If you like 30 Rock, I guarantee you'll like this fic. The humor and dialog are spot-on, and the writer really makes this xover work.

The Great God Pan Is As Dead As Disco (http://community.livejournal.com/presterpress/5763.html) by sophiap (Supernatural/American Gods, gen)
- This is a bit different than the other two, it's a little less cracky and outright, but it's an incredibly intriguing casefic, tying in mythology and the two canons beautifully.

Happy belated birthday!

The first fic that came to mind when I saw your post was See My Vest (http://community.livejournal.com/mollyscribbles/7942.html) by fairest1, a short Harry Potter/Care Bears cracktastic crossover.

untitled Sparkle/Twilight + True Blood/Southern Vampire Chronicle crossover by stoney321
Edward Cullen corresponds with Pam, trying to teach the ways of vampire Mormonism to the wicked wicked Fangtasia crew.
http://stoney321.livejournal.com/377337.html

untitled Supernatural / Labyrinth crossover by fleshflutter
"How the hell was I supposed to know there actually was a goblin king? Let alone that he had a freaking mancrush on me. Though…" Dean cocks his head and considers a moment, "I guess I should have seen that part coming." (implied Dean/Jareth and Sam/Jareth)
http://fleshflutter.livejournal.com/23544.html

DiscTrek series of ficlets by bambiridesagain
The Star Trek Reboot crew finds an very peculiar anomaly, and interact with the people of Discworld.
“Keptin. The anomaly appears to be a… planet… sort of.”
http://bambiridesagain.livejournal.com/3800.html

We Got Some Work To Do Now by atimi
Sam and Dean meet Velma and Daphne and Fred and Shaggy. Hilarity (and sex) ensues. (Sam/Velma, Dean/Daphne/Fred, and Shaggy & Castiel toke up)
http://atimi.livejournal.com/31490.html

A Fucking Space Opera (or Six Characters Who Didn't Board the USS Enterprise) by oxoniensis
[Characters: Arthur Pendragon (Merlin), Rodney McKay (Stargate: Atlantis), Cameron Phillips (Terminator: Sarah Connor Chronicles), Sam and Dean Winchester (Supernatural), and Vanessa the Squid (Harry Potter)]
http://oxoniensis.livejournal.com/411425.html

#krisallenpinkranger by eirana_regan
American Idol RPF/Power Rangers. Allison’s the leader, Matt’s the second-in-command, Anoop’s the smart one, Megan’s the best fighter, and Kris gets held hostage - alot. He’s like the Daphne of the Power Rangers. [Kris = the Pink Ranger, Adam = the Silver Ranger]
http://eirana-regan.livejournal.com/6071.html

Golden by Jerakeen
Wherein Kris and Adam are the Charms and Divination Instructors at Hogwarts (respectively) and they go in to the forbidden forest on the full moon to harvest some esoteric ingredient and Kris is captured by a baby unicorn because Kris is a virgin. Adam decides this will not do at all. Baby unicorns cry at the end of the story.
http://community.livejournal.com/kradam_kiss/56590.html

Hmm... I'm probably copping out on this lol, but what you described... basically my entire delicious bookmarks list.

delicious.com/eponymousanonymous

Plotty:
Five Things That Never Happened to Xanxus, by Lys ap Adin
http://www.branchandroot.net/archive/2009/08/five-things-that-never-happened-to-xanxus/
Katekyo Hitman Reborn. These are things that never happened to Xanxus, but could have done, if only things had started out just a bit differently. This fic is what happens when you say to yourself, "Gosh, I've been writing a lot of Xanxus angst lately. I wonder if it is possible to write Xanxus in such a way that he is, well, functionally broken instead of just psychopathically insane." And then you get tackled by a plot bunny that is the size of a goddamn linebacker.

After you read that, you can go to http://www.branchandroot.net/archive/category/khr/choice/ and read other fic that's inspired by/connected to that first one. They're all excellent. ^_^

Forward Momentum, by BracketyJack
http://bracketyjack.livejournal.com/9482.html
Vorkosigan Saga. This Miles fanfic novel of manners is in canon to A Civil Campaign and Winterfair Gifts, but AU to Diplomatic Immunity. Besides the devil making work for idle hands, and a runaway plot-bunny that most unnaturally mated with a New Year Resolution, it's mostly a result of upending LMB's creative rule of thumb about when in doubt making the worst possible thing happen. Suppose really good things started happening, and Miles was there to run with them...
~175,000 words. This is my comfort fic. ^_^

Embers, by Vathara
http://www.fanfiction.net/s/5398503/1/Embers
Avatar: the Last Airbender. Dragon's fire is not so easily extinguished; when Zuko rediscovers a lost firebending technique, shifting flames can shift the world...
Vathara is amazing, no ifs, ands, or buts. I'd recommend everything she's written, but this is her current work in progress, and it's the best Avatar fanfic I've ever read. It's truly epic in scale, and currently stands at 320,860 words.

Romance:
Captive Prince, by Freece
http://freece.livejournal.com/39701.html
Original fic. Damen is the true heir to the throne, but when his half brother seizes power, Damen is captured, stripped of his identity and sent to serve the prince of a rival nation as a pleasure slave.
I know this sounds like a barrel of cliches, and I suppose in a way it is, but Freece is a spectacular writer with an unfailing talent for characterization and detail. I highly recommend it.

Outlands, by maldoror_gw
http://maldoror-gw.livejournal.com/83190.html
Another excellent original fic. A Japanese businessman stumbles into another dimension and meets an Assyrian warrior. Adventure and romance ensue. Nice world building, interesting non-cliche characterization, and lots of culture clash. The completed first arc works as a complete story.

Cracky/Improbably Xovers and AUs:
Heartless, by sesame_seed
http://sesame-seed.livejournal.com/239891.html
A Loveless/Prince of Tennis fusion, excellently done.

Bloodsport, by Lys ap Adin
http://lysapadin.dreamwidth.org/60591.html
Katekyo Hitman Reborn AU with vampires; angst, violence, fangsex, death. No pairings but plenty of subtext. 27,707 words.
At once hilarious and heartbreaking, with some gorgeous world building.

I have lots more, but I'm afraid that's all I have time for. You might enjoy looking through my delicious account, the_virtual_bookshelf. Especially:
http://delicious.com/the_virtual_bookshelf/awesome-all
http://delicious.com/the_virtual_bookshelf/au
http://delicious.com/the_virtual_bookshelf/crossover
http://delicious.com/the_virtual_bookshelf/fusion

Thank you! ^_^

http://www.wraithbait.com/viewstory.php?sid=3803&warning=12

Hilarious crossover between Stargate Atlantis and Star Trek TOS that had me giggling the whole way through.

One of my favourite fusions is
In the Circle of Elemental Arms by Kryssa's flute
Magic runs strong in the students of Ouran, even in one klutzy scholarship student.
A complete Ouran High School Host Club fusion with elemental abilities, 25 chapter's and 146,588 words long,

http://www.fanfiction.net/s/3581116/1/In_the_Circle_of_Elemental_Arms

One of my favourite Fulmetal alchemist stories with a great twist

Returning Echoes by silkendreammaid
Four years and Edward returns home... with changes. FemEdRoy Read this I don't think you will regret it. So far 37 chapters and 428,372 words

http://www.fanfiction.net/s/3532730/1/Returning_Echoes

And for a great and pretty cracked crossover of Magic Kaito/Kingdom Hearts 2/YGO, with plenty of others along for the ride.

Promenade by Ocianne
MK. "There are more things in Heaven and Earth..." and Kaito's on a trip through all of them. Can he deal with a broody black-cloaked stranger, a stubborn detective, and his world repeatedly turning upside down and still keep what's left of his sanity?

http://www.fanfiction.net/s/2978396/1/Promenade

This is complete with 30 chapters and 170,619 words and a sequel in the prosess. If you haven't come across Magic Kaito or it's related manga Detective Conan, have a look at wiki for both, because then the subtext will be clearer but otherwise still a great read.