At the end of the day (and by this I mean before one retire to ones pit) Kind regards (z) is increasingly common in business usage, "kind regards" and especially "best regards" are often used as a semi-formal valediction in emails. In informal usage, they are often abbreviated to "BR" or "KR". The use of "kind regards" is most likely derived from the more formal, "kindest regards," which is itself a phrase derived from the even more formal combination of "Kindest regards, I remain," "yours" or "truly yours" or any one of a number of valedictions in common usage. My preferred option is the ever warmful "Yours aye", which is a Scottish expression meaning "yours always", the valediction commonly used by members of the armed forces. I have also found that a simple "cheerio" can suffice, or depending on the content of the letter words with the same initial letters as "Foxtrot Oscar" - However, I do like Kind Regardz...........it has a very pleasant feel to it!
Your aye,
Doctor Phaw