Olight had a Ti M20 and JETBeam did the 3M in Ti. Those are the biggest ones I can think of.Very nice. The Fatties have pretty thick Ti. What about something that's more commercially available (ie, non custom lights).
Not sure whether or not you'd call TnC "custom" or not, but their Ti-18650-P60 host is fairly massive ....
Moddoo also make an 18650 titanium P60 host, too.
.... And, of course, the Veleno Designs Thudoo: