The List
There are 369 5 letter words with O as the last letter. The highest scoring is MEZZO at 25 points in Scrabble, though Words With Friends prefers BIZZO at 26. 86 carry three or more vowels, which makes them useful for dumping a vowel-clogged rack.
ABMHOACHOOADDIOADOBOAGGROAGLOOALAMOALTHOAMIDOAMIGOAMINOAMNIOANCHOANDROANGLOAPPROASPROAUDIOAVISOAWATOAWETOAZIDOBABOOBACCOBALOOBANCOBANJOBARDOBARROBASHOBASSOBASTOBAZOOBEANOBENTOBERKOBIFFOBILBOBIMBOBINGOBIZZOBOFFOBOMBOBONGOBORGOBRAVOBROMOBUCKOBUFFOBUMBOBUNCOBUNKOBUROOBURROBUTEOCACAOCAMEOCAMPOCANSOCANTOCARBOCARGOCASCOCELLOCENTOCHACOCHADOCHEMOCHIAOCHICOCHIMOCHINOCHIROCHOCOCHOKOCHOLOCISCOCLAROCOCCOCOMBOCOMMOCOMPOCONDOCONGOCONTOCONVOCORNOCORSOCREDOCUFFOCURIOCUSSOCUTTOCYANOCYCLODAIKODANIODATTODECKODEFFODEKKODERRODIAZODINGODIPSODISCODITTODOBRODOGGODOHYODONKODRACODSOBODSOMODUBBODUMBODUNNODUOMOERUGOESTROFANGOFATSOFIBROFILLOFLEXOFOLIOFORDOFORGOFUEROFUGIOFUNGOGADJOGADSOGALVOGAMBOGARBOGAZOOGECKOGENROGESSOGINZOGIPPOGISMOGIZMOGOBBOGODSOGOMBOGONZOGREBOGREGOGUACOGUANOGUIROGUMBOGUSTOGYPPOHALLOHELIOHELLOHILLOHIMBOHIPPOHOLLOHOWSOHULLOHYDROIGAPOIGLOOIMAGOIMIDOIMINOINTROIROKOJAMBOJELLOJINGOJOCKOJUMBOJUNCOJUNTOKAROOKAZOOKEENOKEMBOKENDOKIDDOKIMBOKONDOKUSSOLAEVOLARGOLASSOLAZZOLENTOLESBOLEUCOLIMBOLINGOLITHOLLANOLOTTOMACHOMACROMAIKOMAMBOMANGOMANTOMATLOMATZOMENTOMESTOMETHOMETROMEZZOMICROMILKOMIMEOMISDOMISGOMOLTOMONDOMONGOMORROMOSSOMOTTOMUCHOMUCROMUNGONACHONAPOONARCONGAIONITRONUTSOORTHOOUTDOOUTGOOUTROOVOLOPAEDOPANKOPANTOPAOLOPAREOPARGOPARVOPASEOPATIOPEDROPENGOPESTOPETTOPHONOPHOTOPIANOPIEZOPILAOPINGOPINKOPINTOPISCOPOLIOPONGOPOSHOPOTOOPOTTOPRIMOPROMOPROSOPROTOPUBCOPULAOPULMOPUNTOPUTTOQUINOQUIPORADIORATIORATOORAUPORAZOOREALORECCORECTOREFFOREGGOREPRORESTORETRORHINORODEOROMEORONDORONEORUMBORUMPOSADDOSALTOSALVOSAMBOSANGOSANKOSANTOSARGOSCHMOSCUDOSECCOSEGNOSERVOSEXTOSHAKOSHISOSICKOSIXMOSKIMOSMOKOSOCKOSOLDOSORBOSORDOSORGOSPADOSTENOSTYLOSULFOTABOOTACHOTAIKOTANGOTANTOTARDOTELCOTEMPOTENNOTHOROTIMBOTONDOTORSOTRIGOTRUGOTURBOTYPTOUREDOVERSOVIDEOVIREOVISTOVULGOWACKOWAHOOWALDOWAZOOWHAMOWHOSOWILCOYAHOOYARCOYARTOYOBBOYUCKOYUMMOZAMBOZHOMOZINCOZIPPOZOCCOZOPPOZORRO