Compilation so far:
Fem-Blaise (Okay, so a guy is a girl in fanfics. Anything else?)
Draco in Leather Pants (see tvtropes)
Marriage Contract (What?)
Soul Bonds (Huh?)
Sorting Ceremony for OC (Sparklypoo??? Is there anything else that goes with it?)
Trelawney's Mysterious New Prophecies (pretty self-explanatory)
Ultra-Powerful Harry (so's this)
Ultra-Mature Harry (and this)
Good centaurs (I guess that's a cliche?)
MoRon (So Ron's not the smartest guy around--anything else?)
Helpful Goblins (like, really helpful or still complete dicks?)
Ancient House of Potter (And so . . . what? I mean, what does this do?)
Other types of magic based around hippy-dippy crystal animal spirit guys in kilts being more powerful than wands (I think that too is self-explanatory and . . . inevitable. I personally blame Charles deLint)
Hermione Granger, Super-Genius (I still think that's basically canon)
Evil Dumbledore (pretty self-explanatory)
Senile Dumbledore (and that)
Evil Senile Dumbledore (okay . . .)
Ron the Death Eater (How'd that come up as a cliche? Geeze. Poor Ron, he really does get the worst of things, doesn't he.)
US Mages integrated with muggles (wait, what? How is that relevant? How'd it even come up? Are there a lot of Harry Potter in America stories?)
Quiddich-trained reflexes (I think I can see how this would be a super-annoying cliche. I imagine Rocky-style training montages.)
Legilimency and occlumency as superpowers (meaning what? I'm not sure I get it)
Divination only about the future (uh huh)
Ancient magic is better than modern magic (the annoying thing is, is that this trope shows up in the canon as well. Maybe not "better" but we never do see
equivalent stuff to the Room of Requirement. Even magic photographs aren't as good as stealing the subject's soul as portraits)
Animagus, metamorphmagus, and parsel-tongue the only rare traits (I think that they are the only rare traits. Except maybe animagus, which people can
learn, they just don't bother to)
Dumbledore letting Snape get away with blatant favoritism (okay)
Snape's hatred of Harry being so great he'll blame anything on him (yeah, but more often than not he's actually right)
Snape's hatred of Harry leading him to look stupid (I sense a pattern)
Timeturners being available to any top tier student (is this a cliche?)
So if people can come up with an explanation to some of these cliches, that'd be great. Marriage contracts and soul bonds, especially
Fem-Blaise (Okay, so a guy is a girl in fanfics. Anything else?)
Draco in Leather Pants (see tvtropes)
Marriage Contract (What?)
Soul Bonds (Huh?)
Sorting Ceremony for OC (Sparklypoo??? Is there anything else that goes with it?)
Trelawney's Mysterious New Prophecies (pretty self-explanatory)
Ultra-Powerful Harry (so's this)
Ultra-Mature Harry (and this)
Good centaurs (I guess that's a cliche?)
MoRon (So Ron's not the smartest guy around--anything else?)
Helpful Goblins (like, really helpful or still complete dicks?)
Ancient House of Potter (And so . . . what? I mean, what does this do?)
Other types of magic based around hippy-dippy crystal animal spirit guys in kilts being more powerful than wands (I think that too is self-explanatory and . . . inevitable. I personally blame Charles deLint)
Hermione Granger, Super-Genius (I still think that's basically canon)
Evil Dumbledore (pretty self-explanatory)
Senile Dumbledore (and that)
Evil Senile Dumbledore (okay . . .)
Ron the Death Eater (How'd that come up as a cliche? Geeze. Poor Ron, he really does get the worst of things, doesn't he.)
US Mages integrated with muggles (wait, what? How is that relevant? How'd it even come up? Are there a lot of Harry Potter in America stories?)
Quiddich-trained reflexes (I think I can see how this would be a super-annoying cliche. I imagine Rocky-style training montages.)
Legilimency and occlumency as superpowers (meaning what? I'm not sure I get it)
Divination only about the future (uh huh)
Ancient magic is better than modern magic (the annoying thing is, is that this trope shows up in the canon as well. Maybe not "better" but we never do see
equivalent stuff to the Room of Requirement. Even magic photographs aren't as good as stealing the subject's soul as portraits)
Animagus, metamorphmagus, and parsel-tongue the only rare traits (I think that they are the only rare traits. Except maybe animagus, which people can
learn, they just don't bother to)
Dumbledore letting Snape get away with blatant favoritism (okay)
Snape's hatred of Harry being so great he'll blame anything on him (yeah, but more often than not he's actually right)
Snape's hatred of Harry leading him to look stupid (I sense a pattern)
Timeturners being available to any top tier student (is this a cliche?)
So if people can come up with an explanation to some of these cliches, that'd be great. Marriage contracts and soul bonds, especially