Im looking for some Opeth songs that are mostly slow acoustic songs such as To bid you Farewell.
Where he actually sings and not screams or growls what ever you want to call it..
alot/some of them have acoustic parts to them...i cant think of any off the top of my head

i cant remember if black rose immortal does, but it might considering its 20mins long
Ah, you want specifically acoustic parts? Didn't spot that.

The clean guitar in those songs should sound just as good on acoustic.
take a look at all the stuff off the Damnation album and also Harvest from Blackwater Park if you're interested in learning the acoustic stuff.

What an outstanding band.
For slower/acoustic ones, besides those already mentioned:

Hope Leaves
Dirge for November (starts slow, then does the death vocals)
Ending Credits

Just get Damnation and you will be satisfied
Also, I dont know if you don't like growls or whatever...but learn to like them, because while their clean material is outstanding, their heavy songs are just unbelievably good. Opeth brings a whole new level of musicianship to the genre.

I like opeth...in case you couldn't tell. Now go get those songs.