Use this formula in second workbook in cell A1
and drag it down:
for Ecxel 2007 or later:
=IFERROR(INDEX([Book1.xlsx]Sheet1!$A:$A,MATCH(B1,[Book1.xlsx]Sheet1!$B:$B,0)),"NEW")
for Excel 2003:
=IF(ISERROR(INDEX([Book1.xls]Sheet1!$A:$A,MATCH(B1,[Book1.xls]Sheet1!$B:$B,0))),
"NEW", INDEX([Book1.xls]Sheet1!$A:$A,MATCH(B1,[Book1.xls]Sheet1!$B:$B,0)))