General:
* String of beads
* Strand of beads
* Collection of beads
* Set of beads
* Assortment of beads
More specific:
* Necklace of beads (if they are meant for jewelry)
* Rosary of beads (if they are used for prayer)
* Garland of beads (if they are used for decoration)
Ultimately, the best collective noun will depend on the specific context and the type of beads you are referring to.