The standard has usually been the head of the player character. This shows a clear relationship between the lives and the character; it's almost as if you literally have 5 of that character, and then when a character dies you now have 4. Often in shooters the lives icon will show a little version of your ship, for the same reason.
Hearts are a common more abstract icon, especially when there is no player character or the player character is not easily representable as a visual icon. Hearts should probably be avoided if you have a health meter in addition to lives, as hearts often indicate health as well as lives.
"Chances" and "tries" are less frequently used in place of "lives", especially in puzzle/ect games where "lives" are abstract as there is no actual player character that is dying. You can also call them continues, but that has a fairly defined meaning. When one uses a continue they generally expect to lose their score, a certain degree of progress (going back to the start of the world/level) and they may expect a game over when running out of continues.
The only other common term I've heard in place of "lives" is "guys." Not always applicable obviously and a bit too colloquial, unless your game trends silly in which case it can be a perfect fit.