Ohio:
Ohio's flag is the only state flag in the pennant shape. All other state flags are rectangular. The seventeen stars represent that Ohio was the 17th state and the flag was adopted in 1902, before Oklahoma was even a state. The red and white circle represents the O is Ohio (pretty inventive, I know) and is also said to signify the buckeye for "The Buckeye State".
Indiana:
According Wikipedia the gold torch represents liberty and enlightenment blah, blah, blah...it's Indiana, honestly who cares (sorry Indiana).
Oklahoma:
Very Native Americany, composed of the Osage Nation buffalo skin shield and seven eagle feathers, which I believe represent the seven tribes that "came" to Oklahoma. It might be of interest to you that the state legislature adopted a salute to the flag in 1982, so next time you run across the Oklahoma flag just say "I salute the flag of the state of Oklahoma: Its symbols of peace unite all people". Short and sweet, what's not to like?
Oregon:
I know what you are thinking, and no Oregon does not have two flags-it has a two sided flag! And yes that is a beaver on the one side. Apparently this is the only two sided state flag in the United States, those crazy liberals are capable of just about anything. The beaver is really a special treat and the little guy/girl represents the Oregon state animal. I hope this means that beavers are to Oregon as armadillos are to Oklahoma because hands down beavers are better. Beavers have the ability to chop down trees with their teeth and then construct their own homes. Armadillos have the ability to dig and walk into to traffic.
