Secretary of the Treasury Snow and US Treasurer Marin did a photo op this week: there was a picture in the Thu 3/6 Boston Globe (and probably other papers) showing them signing a 8-foot-wide replica of a $10 bill. The series number read "Series 2003." The fake serial number was "AA0000---0A" but my guess is the real bills' serials will begin with "D" :-)
I do not know if this is a "Nexgen" bill or just the current design with new signatures at the bottom. I also do not know if the One (which has not been redesigned, as far as I know) will be Series 2003--- or Series 2001A. Probably 2003!