18 Siddhar from Tamil Nadu

1. Nandeeswarar 
2. Tirumular
3. Agathiyar
4. Kalangi Nathar
5. Pathanjali
6. Korakkar
7. Pulipaani
8. Konganar
9. Sattamuni
10. Theraiyar
11. Ramadevar
12. Siva vaakiyar
13. Edaikkadar
14. Machamuni
15. KaruvoorarThevar
16. Bogar
17. Pambatti 
18. Kuthambai

Reference:
http://temple.dinamalar.com/news_detail.php?id=17168
Links to Arab world - http://www.anaadifoundation.org/blog/siddhars/ramadevar-siddhar/
https://en.wikipedia.org/wiki/Siddhar