i'm an atheist, but i did a lot of research on this too before turning atheist ;-)
actually the WT position is "backed up" by only one single verse in the whole bible, ignoring other verses and aplied wrong. the "but the dead don't know anything" verse... don't remember where exactly it is, i think ecclesiastes or proverbs.
iirc this verse really applies to not talking to the dead for informations, as they don't know any more than we do anyway.
bible passages like saul talking to samuel's spirit, hiob referring to sheol as a place of constant work (similar to the greek idea of hades), jesus referring to the afterlife as heaven and hell like the way most christian denominations view it, paulus talking about the 3rd heavens and on and on...
jesus' illustration about lazarus and the rich man always troubled me. they said, it's just an illustration. but why the heck would jesus, talking to jews, use an illustration that's completely unrelated to the culture? i mean, why would he, god's son, tell them about heaven and hell if he actually knows they don't exist?
what really opened my eyes on this one, was flavius josephus' descriptions of the jewish sects. josephus said to have been in all three popular sects (saducees, pharisees and essenes) and stayed with the pharisees in the end. the picture he paints of the pharisees is completely different to the one presented by christians.
but the most interesting part is their believe in an immortal soul that goes to sheol, the underworld. and it becomes even more interesting that paulus, who lived at about the same time as josephus (only born earlier), referred to himself as a PHARISEE when having an argument in the sanhedrin about the resurrection...
so yes, the bible does know the immortal soul. keep in mind though, that it was written by different people, believing different things. so it has a lot of different views. there's no red line from beginning to end as we were always told. it's not there.
it is a very interesting task to research the bible. just be honest to yourself... you might well end up an atheist too ;-)