In my experience, the most overrated "broken" thing would easily be the warlock. I've never gotten a chance to play one. Every DM I've run across just flat-out hates them because they don't fit the sacred D&D convention of using their powers X/day (despite the fact that they get what essentially amounts to a teensy spell list and a single attack per round). But at least the people who complain about the warlock have stopped complaining about how "broken" the monk is because they don't need weapons and armor to be good in a fight...
A close second would have to be
Tome of Battle material. It keeps getting the "just plain wrong for D&D" complaints because of the powers per day thing, and maybe because
the Lord of the Rings didn't have a warblade in it. Whatever- I'm not an anime or video game fan either, but I still think
Tome of Battle does a decent job of being fantasy-themed martial arts.
I used to hate the spiked chain with a passion, but that's because I had four people out of parties of six wanting to make the same half-orc chainfighter build. There was a span of about two years where it seemed like every party had to have a half-orc chainfighter. (Which, incidentally, seems like a local phenomenon.) But that trend gradually died out so now I'm neutral toward it.
Oh yeah... And psionics still gets a bad rap in many ancient gaming circles because of the way psionics were presented in the first edition
Player's Handbook. Apparently an
entirely optional system in a book published thirty years ago makes psionics unsuitable for any D&D game. But in those circles, psionics are still those zonky powers with no thematic connection to the fantasy genre or any sense of balance or purpose... Whatever.
Sorry, I'll stop being a bitter curmudgeon now.
