I'm seeing a definite lack of Arkansas drives in this forum so I feel obligated to represent.
Hwy 7 from Hot Springs to Harrison is a great trip, plenty of curves and hills. Watch the small town speed traps and you'll be fine. You'll occasionally see some VERY nice, fast cars (well, besides your Subaru) to keep you company. For added bonus, check out the drag strip at centerville.
The Pig Trail is Hwy 23 from Ozark until Brashears (Hwy 16). This is a much shorter drive, but pretty intense with the curves and "crooked and steep" sections. Good alternative to taking I-540 and I-40 when going to or from Fayetteville.
Both drives cover the most beautiful (in my opinion) part of the state. Be very careful though, as both drives have curves that are deceptive, and someone not paying attention can end up at the bottom of a ravine.