Only in the event that you already know the recipient should you consider alternatives such as "Kind regards," or "With best wishes," appropriate. If in doubt, stick to "faithfully," or "sincerely,". Also note that in either case, the "Y" of "Yours" is capped, and the "f" or "s" of "faithfully," or "sincerely," respectively is lower_case. Note the comma after both "faithfully," and "sincerely," too. The positioning of the closing phrase differ depending on the format: FBF: Align left, MBF: Align right.
Unlike a typical UK official letter format, the US has a couple of variations, the full block format and modified block format. The former simply means all elements of the letter, from the return address at the top down to the writer's name at the foot, are justified left. the latter, on the other hand, incorporates some elements to the right or centre, rather like the UK official letter format.