I previously compiled a list of BET inhibitors in clinical trials. It is probably outdated. However, I stumbled upon this webpage that has a very good list of 25 clinical and pre-clinical BET inhibitors. It had several that weren't on my prior list, some of which are only pre-clinical. Four that were on my prior list weren't on theirs: GSK2820151, N-methyl-pyrrolidone (NMP), CC-90010 and SF1126. So in total, the two lists include 29 BET inhibitors.

https://ckb.jax.org/drugClass/show?drugClassId=BET++Inhibitor+%28Pan%29