The only word for which I ever had a quibble over the pronunciation was "Isengard," and the pronunciation of the initial I. Frankly, every possibility sounds wrong...
When it came to Elvish, it was grateful to Tolkien for having given Donald Swann his Gregorian Chant-like rendering of "Namarie." As a singer, I've found that music can give one broad strokes as to the correct sound of a language (if not its subtleties), because the rhythm of a tune (a well-written one, at least) places syllabic emphasis where it most naturally falls, and can make the use of incorrect vowel sounds difficult (sometimes downright impossible) to sing. The fact that Tolkien also approved of Swann's renderings of "A Elbereth Gilthoniel" and "In the Willow-Meads of Tasarinan" gives further indications of the rhythm and pronunciations of Elvish, as well as Entish.
Frankly, I don't think I would have ever had any issue over the pronunciation of the hard C if I hadn't heard of the Boston C(S)eltics long before I read LotR, or learned that the word was properly pronounced Keltic. I know an awful lot of people here in the US have that same issue.
