A good choice for a first taste of meditation is the Vipassana Foundation. Regular courses are available on a donation basis. Their main office in Kathmandu with a basement meditation hall is just off Kantipath Road nearby Thamel. The retreat center, Dharma Singha, is on the outskirts of the valley to the north. The center is above a Hindu shrine known as Budhanilkantha and a memorial honoring the late Khaptad Baba. A large golden stupa inside the compound resembles Burma’s famous Schwedagon Pagoda. To find the main office in Kathmandu, follow Kantipath to the right (south) from Tridevi Marg. Within five minutes, there is a complex known as Jyoti Bhawan with both Honda and Hero Honda motorbike sales shops. The office is inside this complex toward the back and the meditation hall is below the office and evening one hour sits begin at 6 PM (5:30 PM in the winter). Courses are run by donation. Visit the Kathmandu Vipassana Centre site for more information. (The retreat center in Pokhara, Dharma Pokhara, is on the outskirts of the valley east, on the southern bank of Begnas Lake, about 18 km from the Lakeside area. Visit http://www.pokhara.dhamma.org/ for further information.)
The International Buddhist Meditation Center Offers also offers instruction in Vipassana meditation, and follows Mahasi Sayadaw style techniques. Room and board are provided (donation based). The center is away from Thamel, and it will take an extra effort to locate the site along the banks of Bagmati River across from Patan in Buddha Nagar, Sankhamul, Kathmandu. Phone 01-4784631 and 4782707 Email: firstname.lastname@example.org.
The Himalayan Buddhist Meditation Center (HBMC) has moved frequently in the last few years and currently, is on the top floor of the Himalayan Yoga Hotel in Thamel (Pokhara's satellite center is up from the north shores of the lake in the hills of an area known as Kahare -roughly 1 km from Hallan Chowk- and offers meditation, yoga, tai-chi, and reiki instruction and regular weekend retreats.)
HBMC also holds regular talks on meditation and Tibetan Buddhism, and is under the auspices of Kopan Monastery in Baudhnath and the Foundation for the Preservation of the Mahayana Tradition.
There are many, majestic Tibetan monasteries near Baudhnath, and most schedule teachings by high lamas and rinpoches as well as standard classes on Buddhist philosophy and Tibetan language, too. The following institutions offer regular courses: the International Buddhist Academy, Rangjung Yeshe Institute, and Kopan Monastery.
Most monasteries in the Baudhnath area of Kathmandu and elsewhere open their doors to visitors. If you visit during daily prayer and chanting ceremonies, you are in for an otherworldly experience, as the sing-song rhythm of the chanting accompanied by bells, conch shell blasts, horns, drums, and cymbals leaves quite an impression. These group prayer ceremonies usually take place in the early morning or early evening. Please respect the setting and do not sit against pillars or on cushions unless invited to do so. You will want to obtain permission before taking photographs of the residents (some of the monks and nuns are quite camera-shy).
Cheers and enjoy your time!
Sidenote--if you are in Thailand and looking for meditation centers, then please try the following link for valuable background information on centers in listed by region of the country: http://www.dhammathai.org/e/meditation/page1.php