There are at least 34 commentaries. Let me try to enumerate as many commentaries as I can. Note that I'm only naming one commentary from each commentator, even if they wrote multiple. And for the most part, I'm only enumerating one commentator from each sect/philosophy, and I'm not enumerating modern books which merely summarize other commentaries.
Now a good starting point is the Dvaita philosopher Narayana Panditacharya's list of 21 commentators on the Brahma Sutras who lived before Madhvacharya:
- Bharativijaya
- Sacchidananda
- Brahmaghosa
- Shatananda
- Udvarta
- Vijaya
- Rudrabhatta
- Vamana
- Yadavaprakasha
- Ramanuja
- Bhartriprapancha
- Dramida
- Brahmadatta
- Bhaskara
- Pishacha
- Vrittikara
- Vijayabhatta
- Vishnukranta
- Vadindra
- Madhavadasa
- Shankara
Note that this list is not in chronological order. Now most of these are lost, and a lot of the lost ones aren't even recognizable. But ten of them are recognizable:
- Baudhayana: He was a shishya and Vyasa wrote the first Vritti or commentary on the Brahma Sutras on the Brahma Sutras, which is now lost. He is traditionally known as the Vrittikara.
- Dramidacharya: He wrote an ancient Bhashya or commentatary on the Brahma Sutras, as well as a commentary on the Chandogya Upanishad, both of which are lost. He is traditionally known as the Bhashyakara.
- Vamana: He wrote an ancient Tika or subcommentary on Dramidacharya's Bhashya, which like the text it comments on is now lost. He is traditionally known as the Tikakara.
- Brahmadatta: He wrote a commentary on the Brahma Sutras which is now lost. He believed that the Jivatma stops existing as a distinct entity upon attaining Moksha, and that lifelong meditation on Brahman is required for Moksha; see page 181.
- Bhatriprapancha: He wrote a commentary advocating a Bhedabheda philosophy that may have been similar to Bhaskaracharya's philosophy of Aupadhika Bhedabheda, which is now lost.
- Adi Shankaracharya: He belonged to the Smartha sect, and he wrote the Brahma Sutra Bhashya, the oldest surviving commentary on the Brahma Sutras, advocating a philosophy called Advaita. You can read it here and here.
- Bhaskaracharya: He wrote the second-oldest surviving commentary on the Brahma Sutras, advocating a philosophy called Aupadhika Bhedabheda. It's never been translated into English, but it's available in print form in Sanskrit here.
- Yadava Prakasha: He wrote a commentary advocating a philosophy called Svabhavika Bhedabheda, which is now lost. He was Ramanujacharya first guru, but then Ramanujacharya left his Ashram and became a Sri Vaishnava, and years later Yadava Prakasha became Ramanujacharya's shishya, renamed as Govinda Jiyar!
- Ramanujacharya: He belonged to the Sri Vaishnava sect, and he wrote the Sri Bhashya, the third-oldest surviving commentary on the Brahma Sutras, advocating a philosophy called Visistadvaita. You can read it here.
- Madhavadasa: He wrote a commentary advocating Advaita, which is now lost. He lost a debate to the Sri Vaishnava Acharya Parashara Bhattar, and then became Parashara Bhattar's chief disciple, renamed as Nanjiyar.
Now here's a list of the rest of the commentators on the Brahma Sutras who are not on Narayana Panditacharya's list, or at least not known to be on the list.
- Srivatsanka Mishra: He lived after Dramidacharya and wrote an ancient commentary on the Brahma Sutras which is now lost.
- Vishnuswami: He belonged to the Rudra Sampradayam of Vaishnavism and wrote the Sarvajna Bhashya, which is now lost.
- Madhvacharya: He founded the Madhwa sect and he wrote the Brahma Sutra Bhashya, advocating a philosophy called Dvaita, which you can read here.
- Srikantha Shivacharya: He belonged to the Shaiva Siddhanta sect and wrote the Srikantha Bhashya, advocating a philosophy called Shiva Vishishtadvaita, which you can read here.
- Sripati Pandita: He belonged to the Veershaiva sect and wrote the Srikara Bhashya, advocating a philosophy called Shakti Visistadvaita, which you can read in Sanskrit here.
- Srinivasa Dikshitar: He belonged to the Vaikhanasa sect and wrote the Lakshmi-Visistadvaita Bhashya, advocating a philosophy called (quell surprise) Lakshmi Visistadvaita, which you can read here.
- Baladeva Vidyabhushana: He belonged to the Gaudiya Vaishnava and wrote the Govinda Bhashya, advocating a philosophy of Achintya Bhedabheda, which you can read here.
- Nimbarkacharya: He belonged to the Kumara Sampradayam of Vaishnavism and wrote the Vedanta Parijata Saurabha, advocating a philosophy called Dvaitadvaita, which you can read here.
- Ramanandacharya: He founded the Ramanandi sect and wrote the Ananda Bhashya, advocating the Ramanandi version of Visistadvaita, which you can read in Sanskrit here, although his authorship is disputed as I discuss here.
- Vijnanabhikshu: He wrote the Vijnanamrita Bhashya, advocating a philosophy called Avibhagadvaita.
- Vallabhacharya: He founded the Pushtimarga sect and wrote the Anubhashya, which advocates a philosophy called Shuddhadvaita, which you can read in Sanskrit here.
- Muktanand Swami: He belonged to the Swaminararayan sect, and wrote a commentary advocating a philosophy called Panchatattva Visistadvaita, which you can read in Sanskrit here
- Shuka: He wrote a commentary using the Bhagavatam to interpret the Brahma Sutras.
Whew!