Short "ow" sound:
* down
* gown
* how
* now
* out
* proud
* town
* vow
* bow (as in "bow and arrow")
Other words with similar vowel sound:
* brown (can be pronounced with a slightly different vowel sound, but still close)
* crown (can be pronounced with a slightly different vowel sound, but still close)
Let me know if you'd like more examples!