I must agree...Z of the Na said:The correct pronunciation for the word is "mon-guh." Two years in Japanese studies taught me that really quick.
I tend to cringe a bit when I hear it pronounced the other way.
After three years of Japanese in High School it hurts my ears when it's pronounced incorrectly.
(After the first few weeks actually)
It's 3 separate syllables : MA-N-GA
MA - as in 'MArio' 'MAMA' 'MArs'
N - as in 'No' 'Never' 'eNd' 'aNNoying"
GA - as in 'GAhh, stop pronouncing it as man-ga!'
So yeah I pronounce it the correct way...MA-N-GA