I would like to have the list of commentators of the Srimad Bhagavatam (the one dedicated to Lord Krishna). How many of these commentaries have being translated to English? Are any of the commentaries available online?
I know of 29 commentaries on the Bhagvatam. This book contains 28 Sanskrit commentaries:
1) Kardama Kshama (Anvaya)
2) Srila Sridhar Swami's Bhavartha-Dipika
3) Srila Vamshidhara's Bhavartha-Dipika-Prakash
4) Srila Jiva Goswami's Vaishnava Toshani
5) Srila Jiva Goswami's Brihad-Vaishnava Toshani
6) Sri Sudarshan Suri's Shukapakshiyam
7) Srila Srinath Chakravarti's Chaitanya Mata Manjusha
8) Srimad Viraraghavacharya's Bhagavat-Chandrika
9) Srimad VijaydhvajTirtha's Pada-Ratnavali
10) Srila Jiva Goswami's Krama-Sandarbha and Brhat Krama-Sandarbha
11) Srila Vishwanath Chakravarti Thakura's Sarartha-Darshini
12) Srila Baladeva Vidyabhushana's Vaishnavanandini
13) Sri Chalarinarayanacharya's Bhagavat Tatparya Tippani
14) Sri Satyabhinavayati's Durghata Bhava Dipika
15) Sri Pandhari Narayanacharya's Durgatoddhara
16) Sri Prabhucharan's Sri Tippani
17) Sri Purushottam Charan's Subodhini Prakash
18) Sri Vallabh Maharaja's Sri Subodhini Lekha
19) Sri Dixit Lalu Bhatta's Subodhini Yojana
20) Sri Bhagavadeeya Nirbhaya Rama Bhatta's Subodhini Karika Vyakhya
21) Sri Ganga Sahay's Anvitartha Prakashika
22) Sri Gopalananda Muni's Nigudhartha Prakash Vyakhyanam
23) Sri BhagavatPrasadacharya's Bhakta Manoranjani
24) Sri Harisuri's Bhakti Rasayanam
25) Sri Shukadev-Acharya's Siddhanta-Pradipa
26) Srimad Vallabhacharya's Subodhini
27) Sri Purushottamcharan Goswami's Subodhini-Prakash
28) Sri GiridharLal Goswami's Balprabodhini
To that list I would add the English commentary written by Srila Prabhupada and his followers, which you can read here. In any case, most of these Sanskrit commentaries haven't been translated into English, except for Vallabhacharya's Subodhini which is available in print form in English here and elsewhere. But it's not available online in English.
But even if these commentaries aren't available in English, we do have the next best thing: the Motilal Banarsidass translation of the Srimad Bhagavatam, which summarizes what different commentators say about each verse. You can read it here.
Though Bhagavan Satya Sai didn't write a full fledged commentary on bhagavatam, he summarized so that even common person can grasp the essence.
He wrote a book named Bhagavata_Vahini which can be downloaded for free from here.