lexipixel - 1:18 am on Dec 14, 2012 (gmt 0)
I always use YYYYMMDD, (and extend it to YYYYMMDDhhmmss based on a 24-hour clock when needed).
19991231 or 19991231235959, (for the last second of the final hour before "Y2K").
Aside from the dates being very clear, they also sort well if you have a column of dates in a table, or a directory full of files prefixed with the YYYYMMDD date, e.g.-
You can always transform to some other format for printing/reporting legibility.