Mis-placed/unnecessary apostrophes are top of my list, or not using them when they should be there.
Dey-ja voo (already you) instead of dey-ja vyu (already seen) for the other language ones. (phonetic spelling there!)
Complimentary and complementary: so often confused/used incorrectly.
Your and you're.
There, they're and their.
And, of course, could of, would of, should of.

There are a few Scots peculiarities too, such as people saying, and spelling the following word as definATEly. And it's quite commonplace to hear "he has went" instead of "he has gone".