rein (as in "free rein")
I suppose that "all right" is a losing battle, because the single-word version has become a legitimate usage, but you'll never catch me writing it. From dictionary.com:
The form alright as a one-word spelling of the phrase all right in all of its senses probably arose by analogy with such words as already and altogether. Although alright is a common spelling in written dialogue and in other types of informal writing, all right is used in more formal, edited writing.
The others seem to be as viruses which have insinuated themselves into the public consciousness-- I was appalled when I recently picked up a 2005 book from the library and found both "you're" and "it's" used as possessives. This has to mean that the original author, the manuscript's editor, the proofreader, and EVERYONE involved in the process of creating this book failed to recognize these as errors.
I'm bothered, not because I think "people should use correct grammar", but because encountering such an obvious and blatant error while I'm trying to read is physically uncomfortable. It makes me feel the same as when I'm eating an apple and accidentally bite into the seed core.