Common Words:
* ran
* red
* rig
* rob
* rot
* rug
* rum
* rye
Less Common Words:
* rao (a unit of land in India)
* raw
* ray
* reb (a type of small boat)
* rex (a king)
* rhy (to rhyme)
* rib
* rip
* rod
* roe (fish eggs)
* rom (a unit of computer memory)
* run
Proper Nouns:
* RPI (Rensselaer Polytechnic Institute)
* RBI (Reserve Bank of India)
Let me know if you need more!