The First Rebirth does spring to mind when I think of hardtrance, Datura tracks, El Sueno & 7th Hallucination live remixes are pretty early also, 93/4ish. Maybe some of the EYE Q/ R&S material, Jam & Spoon or Sven Vath tracks. Its a tough one, different interpretations of hard in the early days, or even which is 'trance' enough to fall into that classification.