Pongal, Makara Sankranti, Lohri
This list is merely indicative, not exhaustive
Probably more indicative of my ignorance than anything else

Pongal , a harvest festival, is THE major holiday in Tamil Nadu, bigger than Deepavali.  It is difficult to think of it as just the “Makara Sankranti” of Tamil Nadu. 
Pongal and cricket matches in Chennai (formerly Madras) are intimately connected.

13/14 January [Last day of Tamil month Margazhi]  

Bhogi Pongal (Tamil Nadu, Andhra Pradesh, Karnataka)

… a night to welcome the sun god…?

Bonfires lit to burn old and discarded household goods, to the beating of drums, Bhogi kottu (Tamil Nadu, Andhra Pradesh)

Uruka day: Assam

Lohri: Punjab, Haryana (til/sesame gajak)

14/15 January [First day of Thai, Makara Sankranti]

… day of the sun god …

Pongal (Tamil Nadu): [newly harvested rice, green gram, sugarcane made into sweet and savoury pongal]

Makara /Poush Sankranti:  Karnataka, Andhra Pradesh, Maharashtra, Gujarat, W Bengal

[people exchange pieces of sugar-cane, molasses, pieces of dry coconut, peanuts and fried gram]

Magh or Bhogali Bihu: Assam 

15/16 January 

Mattu Pongal (Tamil Nadu), Kamumu (Andhra Pradesh): cows and bulls decorated; bullfights (TN – jallikattu, Assam – mohor juj)

16/17 January
A day for seeing the sights:
Kaanum Pongal (Tamil Nadu)

Written in a mood of nostalgia and sense of discovery, sitting in Stony Brook, NY 20 years ago this day. Pongal was the biggest Tamil festival when I left Madras in 1987; much has changed since — Diwali has taken over in Chennai and, increasingly, Tamilnadu.
***Needs a whole lot more! Suggestions and comments most welcome***