This is so sneaky! I am trying to find a good black list and found this:

http://kb.mozillazine.org/Network.IDN.blacklist_chars

Or maybe black listing is not the best approach, maybe a mix of multiple approaches. First strip out stuff and then view the text in a program that displays "unconventional" characters? As a test I pasted the post's test sentences in Vim and the invisible characters are replaced by blocks of <XXXX> that are very hard not to notice. The more you think about it the more tricky corner cases you find :O