I am absolutely positively thrilled to get a story in any of the fandoms I've requested. They're all stories that do mean or have meant a lot to me, and I think you're pretty awesome just for offering to write any of these.
It's Yuletide, and I'll be happy with anything I've requested. I don't want to force your hand, but I'm here to help if you're looking for suggestions or some idea of what I like in fic. First, I'll break it down by request (and as always, they're just suggestions):
Y: The Last Man
I would love something between Yorick and Beth 2 that details some happier times between them. I know that he never really got over realizing how he felt about 355 and then losing her in the worst possible way and that there was definitely a feeling of obligation involved in the relationship and marriage he and Beth 2 had, but it couldn't have been all duty all the time and I'd love to read about some of the times when it wasn't. I'd be just as thrilled to get a story about Hero and Beth 2 on any part of their journey together. I always loved them for what seemed like such a great unlikely friendship that Yorick enabled to blossom between them, but I wouldn't have been surprised if they'd ended up together at the end. I also included Beth Deville because I'd be just as happy with a story exploring any or all aspects of the complicated Beth 2(+Junior)/Yorick/Beth Deville/Hero dynamic that must've happened in the months following their canon reunion.
L M Montgomery - Anne of Green Gables series
I'm almost worried that my lack of suggestions for this request will make you worry that I'm less interested in it than the others, but I promise you that's not the case. The only time I ever read any Anne of Green Gables fic is when I glance through the Yuletide archive, but I'm a sucker for Anne and Gilbert, and as my request said, I'd be thrilled with something sweet and awkward between them. Anything sweet and awkward between them. Set during Anne's time at Redmond would be fantastic, but it's just a possibility that came to mind.
Trigun
My favorite Trigun character is Wolfwood. I'm less familiar with the manga than the anime and I'm not precisely sure how his character differs in the two, but whatever you're most familiar with will work for me. I suggested a day in the life for Wolfwood while he's traveling with Vash because the idea really appeals to me, but I'm easy to please here: anything about their misadventures is cool, and the more Wolfwood the better. Who doesn't love a chain-smoking, motorcycle-riding, gun-slinging priest with a portable confessional. In fact, if all of those things are incorporated into the story, you get bonus points.
Samurai Champloo
You really can't go wrong with a story about the main trio and the hundreds of things that must've happened to them as they traveled through Japan, but if you can write a missing moment type of story about the time Sara spent with them... I would absolutely adore it. I do like the idea of Mugen/Sara, I admit, but I don't need anything to happen that probably didn't happen in canon. I like them the way they were. And if the story's written from the point of view of Mugen, Jin, or Fuu, that's even better.
In general, I like stories that feel like they could've easily happened between chapters or issues or episodes. I have a couple of definite weaknesses: characterization, slice-of-life pieces, scenes in the rain, and really tight friendships forged in unlikely circumstances. And if there's sex, I'd prefer it consensual with no incest and nothing AU.
I hope this helps! And I really hope you just have as much fun writing as I already know I will reading.