Given a list of geographic coordinate pairs, you can implement the Haversine formula directly in Excel.
The simplest way to use this (or a more accurate, but I think it's not your case) formula consists into press
Alt+F11 to open the VBA Editor, click
Insert --> Module and then (copy and) paste e.g. the code kindly suggested by blah238. There will be a new custom
getDistance function available in your spreadsheet which accepts four parameters, i.e. the two pairs of coordinates, as follow:
getDistance(latitude1, longitude1, latitude2, longitude2)
latitude1, longitude1, latitude2, longitude2 should be replaced by their relative cell references.