Virtually every certified aircraft I have ever flown is stable in roll as well as pitch.
AFAIK it is part of the certification requirements.
The only aircraft I have flown apart from a few twitchy permit types that displayed the symptoms IO describes were incorrectly rigged.
In smooth air my Cessna when trimmed will fly for hours in a straight line hands off.
With all due respect peter, it might be worth looking at the rigging on your aircraft if it is rolling like that as it is certainly unusual.