I have a co-worker that swears by
//in a singleton \"Constants\" class
public static final String EMPTY_STRING = \"\";
in a constants class
String literals are interned by default, so no matter how many times you refer to "" in code, there will only be one empty String object. I don't see any benefit in declaring EMPTY_STRING. Otherwise, you might as well declare ONE, TWO, THREE, FOUR, etc. for integer literals.
Of course, if you want to change the value of EMPTY_STRING later, it's handy to have it in one place ;)