After the Duncan I would recommend looking at either BC/What's Next for a wood yo-yo or YoYoJam for a plastic yo-yo.
BC/What's Next is the company that Tom Kuhn (father of the modern yo-yo) merged with and they're one of the few companies still making wood yo-yos.
YoYoJam is the new kid on the block but they make top quality plastic yo-yos, most with ball-bearing axles for a definite step-up from the Duncan.
A third choice might be a Pro-Yo from Playmaxx.
That one is a plastic yo-yo with a wooden axle.
You get the feel of a modern yo-yo with the play of traditional wood.
Of course Duncan still makes yo-yos but apart from their latest model, the Freehand, Duncan has been plagued with quality problems that make a recommendation pretty iffy.
Duncan has just acquired the Playmaxx product line so hopefully these issues will all resolve.
All of these can be found at the above links.
www.yoyodave.com is a sort of front door from which you can get to the discussion board, Daves on-line store, or even Dave's yo-yo museum.