The Insight Meditation Society in Barre, MA offers an annual three-month retreat from Sept - Dec, with some spaces for those who would like to attend for 6 weeks.
Spirit Rock Meditation Center in Woodacre, CA offers an annual two-month retreat in Feb - March, with some spaces for those who would like to attend for 1 month.
The Tathagata Meditation Center in San Jose, CA hosts monastics from the Mahasi Sayadaw lineage, and offers teachings and retreats online and in person.
Vipassana Metta on Maui teachers Steve Armstrong and Kamala Masters offer Mahasi style retreats at centers in the USA and internationally.
Ven. Vivekanada, a western monk trained by Sayadaw U Pandita, and resident teacher at Panditarama Lumbini, also offers some retreats in the west.
The Saddhamma Foundation organizes 2-month retreats for westerners at the center founded by the late Sayadaw U Pandita in Myanmar (Burma), about 2 hours from Yangon.
Vipassana Hawai'i organizes 3-week retreats for westerners at the historic Kyaswa Monastery outside of Mandaly in Myanmar (Burma).
Panditarama Lumbini in Nepal offers opportunites to practice with monastics from the Mahasi Sayadaw lineage.
Bhavana Society in High View, WV founded by the venerable Bhante Gunaratana, offers teachings and retreats online and in person.
Dassanaya Buddhist Community in Alexandria, VA maintains a small center led by Ayya Dhammadipa, a fully ordained Theravadin nun.
Ky Vien Tu (Jetavana Vihara Temple) in Washington, DC maintains a small center established by Bhante Khippapanno, a Vietnamese monk who trained with Mahasi Sayadaw.