It's very rare that I am asked to do it, but I found that given a little experimentation with the various settings, Izotope's Radius can provide some convincing results whilst keeping the pitch intact.
I hate any plugin for this that I have tried - can hear the difference even with very small bpm changes - just sounds unnatural and glitchy.
Varispeed from DAT/CD before any processing is a preferable option (unless you don't want to pitch shift), but there is something better - I can't for the life of me remember the piece of analogue outboard that time stretches without pitch shift - anyone? Rare as that stuff that comes out of rocking horses....
Hey Alecio - try Reaper, it has great stretching algoriddim 'Dirac LE'. At its maximal settings this algo beats all other algos I have tried. It is very slow and does not work in realtime, but we do care here about quality, not speed.