I've used the Big Stubby line of picks for probably fifteen years as an option for a truly thick and easy to grip pick.  These picks are by no means for everyone, as they provide a level of thickness that really goes beyond any worry of the pick flexing.  These are very usable for guitar and bass and their thickness provides fantastic durability.  Between the 1.0mm, 2.0mm, and 3.0mm options, you can probably find something you'll like, provided you enjoy the unique indentation grip--and the general feeling of ridiculousness that goes with using such a thick pick.