Oklahoma is a OK...as long as you're not expecting too much from the online content of the Oklahoma State Archives.
There's a modest amount of good digital stuff to be found here.
A selection of archived Collection Highlights has descriptions of mostly offline content, but one worthwhile online document:
Index to Oklahoma Confederate Pension Records includes full name, spouse's name, date of death, and microfilm identifcation information.
At the Oklahoma Digital Prairie you'll find diverse collections of documents, images and artifacts, including:
At the Oklahoma Historical Society you'll find yet more descriptions of offline materials, along with a few nice online gems, especially for family history research: