Lord Baladeva's Appearance:
On the purnima or full moon of the month of Sridhara month Balarama, the elder brother of Lord Krsna appeared. This day is celebrated in Vrndavana and Mathura region. Particularly at the Dauji Temple, where Balarama resides with His consort Revati.
One may perform worship with abhiseka as for Sri Krsna Janmastami.
The Pastimes of Lord Balaram condensed for Class:
Prayers to Lord Balaram - Avatara.org
Verses in Praise of Lord Balaram:
Balaramavatara - Indian Heritage site:
Lord Balaram Deity on the beach at Malpe - originally carved by Vishvakarma from a Shaligram.
Sri Gopal Tapani Upanishad on why Lord Balaram appeared: