The Reproaches is a hymn found in the Roman Missal that is appropriate for being sung during the veneration of the Cross. The Latin version can be found on page 311 of the Gregorian Missal (download it here). There are two English versions by Fr. Samuel F. Weber that can be downloaded here (see pages 4 and 8). Another English version.
The videos below will give you a feel for what the Latin version sounds like. There are individual files for the different sections in the Latin version here.
First Half of The Reproaches (Latin)
Second Half of the Reproaches (Latin)
The Reproaches (Latin) - Beginning