The Vineyard is a church-planting movement, conservative evangelical in doctrine but open to the gifts and ministry of the Holy Spirit in a way more commonly associated with the Pentecostal and Charismatic movements. The term Third Wave has sometimes been applied to churches similar to the Vineyard - the idea being that Pentecostalism was the first wave (in the twentieth century) and the charismatic movement the second. John Wimber, the founder of the Vineyard movement as we know it today, wrote that the three "waves" were more similar than different and tended to see them more as different phases of one wave.
Vineyard International has links to the various national Vineyard associations.
Vineyard USA has information about the movement in general, its beliefs, history, and churches in the USA.
The movement has seen more than its fair share of controversy, so here's my page for Vineyard Apologetics.