Moving from West to East -- 

Keylong  (3080 m)
Keylong is the biggest town and administrative headquarter of Lahaul. It is 125 kms away from Manali. Located on Leh-Manali Highway, this town has a strategic importance, thus it is popular among tourist. Many government and private guesthouse and hotels can be found here. One has to cross Rohtang pass to reach Keylong. Therefore, this town remains cutoff from the rest of the world for around 5-6 months from November to May in winters due to heavy snow. 

Kunzum La / Pass (4,550 m / 14,931 ft)
This is the gateway to Spiti valley from Lahaul.  One has to cross Rohtang La and then Kunzum La to enter Spiti from Manali. Bara-Sigri Glacier, the second largest in the world, can be seen from Kunzum La. The top of the valley offers a spectacular landscape with majestic Chandra Bhaga ranges surrounding it on the north sides with snow clapped peaks and massive glaciers threatening to block the valley any moment.The other side is the Spiti valley with its dessert like terrain.
Tourists are advised not to stay here for long. The Nearest  village is Losar (16 kms). 

Chandra Taal (4270m)
Located in Lahaul region, this is one the most beautiful lakes in the entire Himalayas. It means The lake of Moon. This deep blue water lake has a circumferences of 2.5 km. This is also the source of River Chandra.  The surrounding mountains peaks with snow caps and slopes around the valley rise up to 3000 meters to 6300 meters. This crystal clear blue water lake lies in a broad grassy plain, which in ancient times was a glacier, Idle for camping and photography. The mountain ranges are called Moulkila and Chandrabhaga which challenge mountaineers.

Kaza (3,600 m)
The biggest town in Spiti also has the administrative headquarters of Spiti.  Earlier it was the capital of Nono, the Chief of Spiti. Situated at the bank of River Spiti, this town also have famous monastery and temple. Kaza and its nearby village has good accommodation and other facilities like Petrol/Diesel pumps. Being the largest town of the area locals frequently visit it for marketing for daily necessities.

Kye Monastery (4,166 m)
This is the main research centre of the Buddhists in India. It is oldest and biggest monastery in Spiti. It houses the rare painting and beautiful scriptures of Buddha and other gods and goddess. Rare 'Thangkas' (paintings) and ancient musical instruments 'trumpets, cymbals, and drums can be found in the monastery. Many lamas receive their religious training from this monastery. 
Just drive ahead from Key Monastery to reach this village. Trek to the famous Tso Moriri (lake) starts from this village. While the folks stay all year in Kibber, the villagers move down from the other villages to warmer locations during winter. 

A village in Spiti which has the highest post office in the world. For details, read this - or watch this video

Komic (4587 m) 
It takes around 1 hour from Kaza to reach Komic, the highest village in the world which is connected by motorable road. Near by villages -  Hikkim and Langza. All of them look similar as the houses are built in the Tibetan architectural style. Agriculture is the main source of livelihood. Potato farming is common. 

Tabo (3,050 m)
Situated on the left bank of river Spiti, Tabo is in the south of Spiti. While coming from Shimla and Kinnaur Tabo is the gateway to Spiti valley.  Flanked on either sides by hills, its has one of the most important Buddhist monasteries regarded by many as only next to the Tholing Gompa in Tibet. It is also known as the Ajanta of the Himalayas. Tabo is the largest monastic complex of Spiti which has since been declared a protected monument under the aegis of Archaeological Survey of India (ASI).
The famous Dhankar monastery (3890 m) is located 25 kms from Tabo.

Pin Valley 
A Beautiful valley which is also home to the rare himalayan snow leapord and ibex. This valley has several beautiful and important monasteries.