Hello John,
Keep in mind I've only spend a couple days birding in OK. Sooner Lake on the west side of the lake is one of the most relaible. It is where I got my Smith's Longspurs. They tend to stay in the grass though, so not easy to see at first. LeConte's Sparrows are there as well, usually in cattails, also tends to stay in vegetation. Apparently there are some spots where they get Smith's Longspurs just outside of Oklahoma City, but we didn't see them there. They tend to want to keep most of the activity on here about Colorado birds, but I would be happy to give you information about a couple other spots via email.
Ben Sampson,
Boulder, CO