I think it means 'safe bets', referring to acts who are bound to be recognised and go down well (in contrast to the 'pepites de l'underground' which won't be widely recognised).

Carolize, it would be kind of you to include the full sentence you inquire about in your question. If you don't, I have to go listen to the entire exercise myself. I find this very inconvenient and time consuming. Please, next time, post the entire sentence under question.

Pardon, la phrase complète: "Légendes du métal, pépites de l'underground et valeurs sûres se déchaînent sur scène, dans un déferlement d'effets pyrotechniques et autres prouesses spectaculaires, pour la plus grande joie des festivaliers qui ne boudent pas leur plaisir !"

Yes, Tom's right: valeurs sûrs in this context means something like "crowd pleasers".