Not this argument again.. LOL

Sephiroth:
Sef-a-roth

Cait Sith: (never had arguments over this one)
Kate Sith

Aeris:
Air-iss

Yuffie: (Like Yiffie with a U!)
Yuh-fee

Rinoa:
Rih-no-ah

Seifer:
See-fur

Eiko: (How the Ei in Eiko is different than Seifer is beyond be)
EEk-o

Zidane: (again, never got controversy over this one)
Zid-ayn

Brahne:
Bron (Rhymes with John, Don and Con)

Eidolon: (This actual non-FF word comes from Greek and thusly pronounced as such. English Ei rule doesn't apply)
"I"-doh-lon

Tidus:
Tie-dus

Chocbo: (I used to say it like Strawberryman and Faith also)
Cho-ko-bo

Bahamut: (I'm wrong on mine.. its local dialect that screws this for me. No persecutions please)
Bah-hum-it

Another controversial name:

Steiner: (Steiner is German and is pronounced as if it were German. I know people with this as their last name and they all say it like I do.)
Sty-ner