the correct one is "è" which in english means "is". there are no other possibilities.

" è " accented letter (only at the end of words like "perchè" = why/because) " é " verb to be (is) " e' " serious grammatical error " e " conjunction (and)

If we are talking solely about the two accents, è [ɛ] and é [e], I agree that only "è" is valid. If however, you are talking about the applications of the two accents, then "é" is also available in some words, such as perché ("why/because"), in ambiguous monosyllables such as né ("neither") versus ne ("of it") and sé ("itself") versus se ("if"). 　 Online reference: http://en.wikipedia.org/wiki/Acute_accent (look for the Italian part)　

The sign ' is an apostrophe and not an accent, but due to the large diffusion of American or English keyboards especially among programmers, the use of the sign ' instead of the proper accent is tolerated, and the reader is left with the task of changing the graphics of the sign in his mind; This 'low-level' standard is obviously not ok in books, newspapers, etc.