As far as 4x4 in general, I don't know of Fayetteville/Springdale, but in Bentonville, you have 2 options I know of :
For parts (90% of which you can order online for less) and bolt-on installs (about 50-75% of which you can probably do in your garage/driveway with limited power tools), there is 4WheelConcepts : http://www.4wheelconcepts.com/
They sort of have a bad rep of being started by some rich daddy's boy wheeler that wanted his own shop, but I've never personally heard anything negative about their work, in particular.
For you hardcore needs, including fabrication and the deep down building, only one place to go...Bohannans : [ame="http://maps.google.com/maps?hl=en&q=616+S.+Main+St+bentonville,+ar&um=1&i e=UTF-8&sa=X&oi=geocode_result&resnum=1&ct=title"]Bohannan's location on GoogleMaps[/ame]. They don't have a website as far as I can tell, and if you pull up to the shop, you might not even know you're there unless they have their usual 4 or 5 Jeeps sitting out front, but from what I've seen, there isn't much they can't do with a rig. I've seen CJs, YJs, TJs, XJs, and FJs (yup, them too) sitting out front, built up, as well as a few others that don't have cool designators to refer to them by.
Those are the two main shops I know of in the area. For basic DIY bolt-ons and what not, if you aren't comfortable tearing into your rig too much, your best bet is to do as many meet&greets as you can on here...it won't take long before you start to rub elbows with some very capable wrenchers on here that will usually have no problem showing a new guy a few tricks.