The letter combinations/pairing of: o_e, oa, ow, oe can also make the long "o" sound. Here is an interesting "o" word for you, did you know the name for "pound" key (#) it's "octothrope". I guess hashtags weren't a thing when they dreamt up that word. Another cool fact, the word "dreamt" is the only English word to end with the letters "mt".
The most common long a words are: go, so, no, bone, joke, rose, close, boat and soap. The most common short a words are: cop, dog, hot, jog, mom, mop, pot, son and won.