The List
There are 209 4 letter words with O as the last letter. The highest scoring is DZHO at 17 points in Scrabble, though Words With Friends prefers JUCO at 17. 11 carry three or more vowels, which makes them useful for dumping a vowel-clogged rack.
AEROAFROAGIOALCOALKOALOOALSOALTOAMBOAMMOANNOAPSOARCOARVOAUTOBEGOBIROBITOBOHOBOKOBOLOBOYOBOZOBRIOBROOBUBOBUDOBUFOCALOCAMOCAPOCEROCHAOCIAOCITOCOCOCOHODADODAGODATODECODEFODELODEMODERODIDODINODIVODOCODODODOJODURODZHOECCOECHOEDDOERGOEUROEXPOFADOFANOFAROFICOFIDOFIGOFILOFINOGAJOGAPOGIROGOBOGOGOGYROHALOHAROHELOHEROHOBOHUSOHYPOINFOINGOINROINTOJATOJIAOJOCOJOMOJUCOJUDOKAGOKAROKAYOKENOKEROKETOKILOKINOKOBOKOLOKOROKOTOKUDOKYBOLAZOLENOLEVOLIDOLILOLIMOLINOLIPOLOBOLOCOLOGOLOTOLUDOMAKOMANOMAYOMEMOMENOMICOMILOMINOMIROMISOMOJOMOKOMONOMOZOMUSOMYXONOLOODSOOLEOOLIOONTOOPPOORDOORZOOTTOOUZOPACOPEPOPESOPISOPOCOPOGOPOLOPOMOPRAOPROOPYRORATOREDOREGOREPORIVOROTOSADOSAGOSECOSEGOSHMOSHOOSIJOSILOSKEOSKIOSOHOSOLOSUGOSUMOSYBOTACOTAROTHIOTHROTIROTOCOTOHOTOKOTOMOTOPOTOROTOYOTRIOTYPOTYROUMBOUNCOUNDOUNTOUPDOUPGOURAOVEGOVETOVINOVIVOWEROWHIOWINOYEBOYOYOYUKOZEROZOBO