Above & Beyond - On My Way to Heaven. Still one of the best examples of what "modern trance" could have sounded like without plucks and saws. One of the more unique A&B productions.
Cass & Slide - Perception (Vocal mix)
No need to mention Beautiful Things/As the Rush Comes, but I personally wouldn't rate them as high as the other tracks on the list.
Libra - Calling Your Name (Ferry Corsten Remix)
Oakenfold - Southern Sun
Lange - Happiness Happening
Underworld - Born Slippy
Ascension - Someone
If I had to vote on what the best vocal tracks ever made I would say Silence. It's not often you get such a hugely popular track that is actually good and still enjoyable to listen to today, despite the 100 times I've heard it. I still get great emotions when I play it and I don't think any other Trance track reached the heights this one did. Southern Sun would be a close second.
There's another category of vocal tracks that I wouldn't necessarily label Vocal Trance but are worth mentioning because its a completely lost art in Trance and Progressive music and that's when the vocal part would be more of a instrument in of itself, with no lyrics but simply to the atmosphere and harmonies of the track. I will never understand producers abandoned doing this with modern tracks. It's a completely unique and beautiful Trance thing. One more type of execution would be when the vocals are used in an an iconic and effective way for just a short part of the track, like Lost Tribe - Angel. I wouldn't call that a vocal track but the vocals certainly made it iconic. Some amazing instrumental vocals;
FSOL - Papau New Guinea
Chicane - Saltwater
Scott Bond, Charlie Walker - Naked Angel
Orbital - Halycon On and On
Orkidea - Unity
P.O.S - Gravity
(There's many more i'm forgetting)