So far I am just using this account to track stories I like.
I am currently working on a Harry Potter - Nasuverse (Fate, Tsukihime) crossover but it is slow going. I currently have first 6 chapters (30k words) finished and edited along with pieces of the next few but will not be posting it until I'm done with the prologue (8 chapters long, ends when Harry begins Hogwarts). Trying to find the best way to include a bunch of exposition and deal with some problems from cannon potterverse while keeping the story interesting and keeping the prologue to a reasonable length. It should pick up once I get Harry to school, have some fun ideas for that. The basic outline for the story is complete- and it will be a long one- I just have to fill in the details. I will most likely publish the first 10 chapters together once I complete them (probably in December, it's a busy semester).
I will also be assisting my younger sister on a One Piece story that has the potential to be good, but will not be starting on that one until after I graduate in 2 weeks.
Fate/Stay Night- This one is really fun and is very complex. Great potential for good stories, From Fake Dreams is the best. I still need to play the VN, it is sitting on my computer downloaded but I only just passed the prologue (and that was months ago).
Naruto- While I am not too fond of canon (it eventually became shark-jumpy), it is a great sandbox for fanfiction. There are a number of interesting stories and many ways to approach this world. There are even more crap stories, then again 90% or more of everything on this site is crap (badly written, terrible grammar, boring/uninteresting/strictly canon).
Bleach- This show started out so well, and has been slowly dying ever since. I finally caught up by reading the last 30 chapters and basically nothing has happened! What the heck is up with how powerful the Quincy dudes are anyway? The power creep in Bleach is terrible, it should be more like Hunter x Hunter when it comes to power. Instead of the whole "power levels" type DBZ thing, skill should be far more important (see: Hisoka. Odd skills with apparently little direct combat applicability, stupidly strong). When will it finally end? Still the characters are interesting, their designs great, and powers quite varied. Great fanfiction potential, but there have not been too many good Bleach stories written recently.
Highschool DxD- I'm not sure what it is about these stories, but I quite like them. I've never watched the anime and have only read the first few light novels (through the Phenex arc), but there are some really good DxD stories out there. My favorite is A Demon Lord's Hero (also a Fate crossover which makes it even better).
Harry Potter- There is so much written for it that some of it has to be great (and some of it is). As a children's story HP is amazing, when viewed critically it falls apart at the seams and there are so many ways to fill in those holes and change things.
One Piece- My favorite anime/manga, but not my favorite fandom. The One Piece stories just lack something. Perhaps it is because the source material is already so good so fan fiction looks bad in comparison. There are some good stories but I wish the One Piece writers would try a bit harder. Rehashing canon with an extra character or two is not fun- if you are going to change things by adding additional main characters there should be increasingly significant deviations over time. Following canon to the letter is not only boring but also bad writing.
My Hero Academia- This is a manga I discovered a few weeks ago and it is great (Tsuyu is best girl)! It'll be getting an anime next year and hopefully that will bring it to the attention of a wider audience. There are a full 23 stories right now, but it has the potential to become one of the better Shonen series (replacing the dead-but-not-really-because-side-stories Naruto as one of the "Big 3"?) Hopefully it will gain a strong following and some quality fanfics will be created- it is an excellent sandbox.