Words with "o":
* box
* fox
* hot
* hop
* knock
* lot
* sock
* stop
* top
* watch (the "o" sounds like a short "u" in this word)
Words with other letters:
* blood
* come
* done
* love
* money
* son
* some
* ton
* young
This is not an exhaustive list, but it gives you a good starting point. The vowel sound in "lock" is a bit tricky because it can be spelled with different letters.