The Panguni Uthiram festival is celebrated for 4 main reasons.

1. The marriage of Shiva and Parvathi
2. The union of Lord Muruga and Deivayanai
3. The incarnation of Lord Ayyapa
4. Again the marriage of Ram and Seetha, Radha Krishna.

Devotees visit the temples of any of these Deities to celebrate Panguni Uthiram.  Below are few  Temples where Panguni Uthiram is celebrated.

Shiva

1. Mylapore kapaleeswarar temple
2. Perur patteeswarar Swamy temple

Muruga

1. Arupadai veedu temples of Muruga
2. Viralimalai Murugan Temple
3. Vadapalani Murugan Temple
4. Kundrathur Murugan Temple
5. Vallakootai Murugan Temple
6. Singapore Murugan Temple
7. Malaysia Murugan Temple
8. Sri Lanka Murugan Temple
9. Chennimalai Murugan temple
10. Mailam Murugan temple  (Info by Mr. Raja Venugopal)

Vishnu

1. Sriranganathar Temple

2. Srivilliputhur Temple

Ayyapa

1. A Puram Ayyapan temple (opp to Chettinad Vidhyashram)
2. Sabarimalai Ayyapan temple

Others

1. Kula Vilakkamman Temple
2. Karkuvel Ayyanar Temple

Dear Readers, please add (in the comments session)  more temples where Panguni uthiram is celebrated.