Starting with "ar":
* Arbor
* Ardor
* Arid
* Armor
* Arrow
* Arson
* Artist
Ending with "ar":
* Collar
* Dollar
* Guitar
* Scholar
* Solar
* Sugar
* Wharves
Containing "ar" in the middle:
* Barking
* Carving
* Darling
* Farming
* Marking
* Sparking
* Starling
This is just a small sample, there are many more words out there!