I can't think of any major party in the developed world that is worse than the U.S. Republican Party.
The GOP has some pretty vile elements and has been on a long downward spiral for some time, but how is it worse than actual fascist parties like Jobbik and Golden Dawn?
Are these major parties? Do they hold power? Do they affect policy-making at the highest levels? And besides, until you mentioned them, I never heard of them.
Jobbik and Golden Dawn are significant in their relative countries (Hungary and Greece, respectively), but they're still third parties who have never and probably never will form a government, although they do matter in multi-party systems like Greece and Hungary.
Anyway, if we're considering "parties which have a chance of forming government" as major and limiting it to only democratic systems:
Fidesz (Hungary)
Republican Party (United States)
BJP (India)
ANC (extremely sad to put them on this list, but in their modern form they count)
LDP (Japan)
PRI (Mexico)
Likud (Israel)
The above are in no particular order. There are probably more that I'm not thinking of right now.
