Something like comm but for Windows (No, installing Cygwin just for this is not a good idea.) It will be great if it will allow compare more than 2 files at once. Example for 2 files:
File1:
foo1
foo2
foo3
bar
File2:
bar
foo2
Output:
foo2
bar
(or in reverse order). Whitespace not have to be ignored (but it can), it's already normalized.