Try babynames.com?
but lets see there is:
Ophelia, Olivia, Otie, Opal
Those are the only ones i kind of liked, haha. the other ones looked like they were random names.. that were foreign
O.J. Simpson
Louis Oostuizen
okra
Some objects that end with the letter O are:ammoavocadobamboobanjobistrobuffalocameocellocockatoocuckoodingodominoembryofoliofrescogauchogazebogumboherohippohoboigloojalapenokangarookazoolassolimomangomemonachoOreopalmettopatiopesopestophotopianopiccolopimentopintopistachioPlutoradiorhinosilotacotarotobaccotuxedovideovolcanoyo yozoo
Three: Ohio Oregon Oklahoma (I assume you are talking about states in the US.)
Oreo
The names of cars start with letters of the alphabet. Some of the names are Acura, Chevrolet, Kia and Toyota.
O.J. Simpson
Olivia odelia Oprah opal ondrea ocean oceana odette octavia Orysia, Oxcania, Onyeka,
orioles
Ouzo
oliver, olivia, ozzie, oz.
octopus, ocelot, orca,
oak tree Okame Cherry
Obi-Wan
Louis Oostuizen
Some names that have the long O sound are: Cody Mona Lolita Hobart Jody