I would add 'Jam El Mar' (Dance 2 Trance / Jam & Spoon) on the list, he made the first worldwide Trance hits like 'Stella', 'We Came In Peace' or 'The Age Of Love Remix'... in those times you had very different tunes played in the clubs of UK, Germany or Italy.. most of the releases never really made it outside of their countries, but Jam made his success really internationaly.
Also 'Cosmic Baby' was super popular from 1990-1995, he played only live shows with his keyboards and he was the first 'face' in the faceless underground Trance scene (interviews in TV and magazines), all of his early albums were very positively reviewed.
'Sven Väth' and 'Talla 2XLC' are commercially the most succesful Trance djs/promoters of the early 90's. Sven made the genre popoular with his 'Omen' club and with the legendary 'Eye Q' releases (Cygnus X, Energy 52, B-Zet). Talla's Technoclub parties at the 'Dorian Gray' club played the key role in Frankfurt's Trance scene, also his label 'Suck Me Plasma' was very respected (he signed 'Dance 2 Trance - We Came In Peace').
'Robert Leiner' (The Source Experience), 'Oliver Lieb' (L.S.G.) and also 'Art Of Trance' or 'Sven Van Hees', the TOP producer's of the 90's, just look at their discographies.. high quality..
I wonder that nobody included 'Robert Miles' because his musical touch really changed the substance of Trance music .. what everybody calls now Trance, is more his creation
EDIT: no I can't make a TOP 20 list