I am curious to know as how many popular Christian sects exists that do not belive in Trinity.
I know the JW does not accept Trinity. But am not aware of any other.

The Ebionites were the earliest sect not to accept the Trinity, if we exclude the first disciples who continued to practice Judaism. (Sort of a repudiation of Paul). I am not aware of any other sects of any size today which are not Trinitarian.

I think there are many Christian that do not believe in Trinity but they have not grouped themselves into any sect. Famous examples would include Sir Issac Newton.

As the name implies, Unitarian Universalists don't believe in the Trinity.

'Unitarian Universalism is a centuries-old, free thinking liberal religion guided by shared values.' Possibly many Christians would say that Unitarian Universalists are so free-thinking and ecumenical that they don't count as 'proper' Christians.

Famous Unitarians