Starting with "O"
* Ocean
* Olive
* Omen
* Outrageous
* Only
* Often
* Orbit
* Overjoyed
* Opportunity
Starting with "Or"
* Orchard
* Orchid
* Order
* Organize
* Original
* Ornate
Starting with "Oran"
* Orangutan
These are just a few examples, and you can come up with many more!