Can't really say one of the top of my head but the Cardcaptor Sakura movie was nearly unwatchable for me because the CHANGED THE DUBBING ACTRESS FOR SAKURA, THE MAIN CHARACTER.
I hear that a lot of dubs made in Campinas are bad but I never bothered to check them, so can't really say anything
Other than that, I see more problems with production than the dubbing voices.
Bleach had a very messy dub production with lots of actors changing all the time for a lot of non-regular characters, Rurouni Kenshin (Samurai X) had similar issues with one character (Aoshi).
Patlabor had an ATROUCIOUSLY BAD script that changed what the original text said and messed up translations.
Nadesico had a very low quality translation (they used the english/american localization as a basis).
Wdym? Aside from something here and there, dubbing in Brazil is mostly well done and consistent even saving some bad anime (like Gantz) or movies (like White Chicks).
Dubbing fans on the other hand can be VERY toxic and obnoxious