AppleInsider presents some compelling evidence that mid-September may be date to watch for a new crop of nanos or nano replacements.

AI reports "inventory management systems tied to at least one US-based big-box retailer are reflecting end-of-life notices for Apple's entire iPod nano product line on September 16th", and that September 16th is the date that Apple's "Free iPod nano" back-to-school promotion will expire. This is also consistent with the general time frame previous rumors put forth.