Because there is no single pagan religion, there is no single pagan calendar. The Baltic calendar is different from the Celtic, and both are different from, for instance, the Germanic. But there are four main festivals that were observed rather widely and are still celebrated by neo-pagans today.
Imbolc (February 1st)
This festival seems to be linked to the lactation of the ewes and the birth of the first lambs. It was the sacred day of Brigit (later adopted by the Christian Church as Saint Brigid), the goddess of healing and poetry, especially called upon during times of childbirth.
Beltain (May 1st)
This feast, associated with the new warmth of the sun, is often called the festival of Good Fire. This Irish festival, perhaps recognized in Welsh tales as well, is widely celebrated today. Fires were lit. Cattle were driven through the smoke to purify them. Brave people leaped through the flames with wild abandon, probably after the consumption of a lot of mead. This was the special time when the gods communicated with the world of humans. It may have received its name from the association with the sun god Belenos, who was worshiped in Gaul and Italy. The festival is kept alive today when we remember to dance around maypoles and deliver May baskets.
Lughnasa (August 1st)
Named after Lugh, the god of light, this harvest festival marked the baking of the first bread from new grain. It was a time for dancing outside in the moonlight and festive celebration of the harvest. The stage play and 1998 motion picture Dancing at Lughnasa eloquently capture the wild abandon still felt in rural Ireland during this festival.
Samhain (November 1st)
Perhaps the most important festival of the year, Samhain (pronounced sowen) marked the date the flocks were gathered together and harvested. It celebrated death and renewal. On this day the barrier was stretched thin between the otherworld and the world of humans. Kept alive today at Halloween, this festival was a night for spirits who needed to be placated lest they play their tricks. The tribes were gathered together. Winter was right around the corner. It was a solemn time, a holy but fearsome night.
Besides these festivals, most neo-pagans celebrate the equinoxes and solstices as well, further dividing the year into the traditional seasons of winter, spring, summer, and fall.
Most of the customs originating from these festivals have been both adopted and adapted by the Christian Church. The Celts and Gauls became Romans. The Romans became Christian. But the common people remembered the old ways. The Church, bowing to the inevitable, simply baptized the festivals and brought them into the sanctuary, where we now celebrate Christmas with Yule logs and evergreen trees, and Easter with bunnies and eggs.
From The Religion Book: Places, Prophets, Saints, and Seers by Jim Willis, (c) 2004 Visible Ink Press(R).