Around here, it's the aforementioned Vittoria Zaffiro currently $14, Michelin dynamic (were $13 a couple years ago when I got a 3-pack, but they recently shot up to $20), Innova Skyline $13.
Never tried the Skylines, but the Zaffiros are a hair better than the Dynamics in the grip department. My best score of late was Panaracer Stradius sport 26mm for $10 at a swap meet - much grippier than the Zaffiros.
About 5 years ago I got some IRC Red Storm on sale for $10 apiece, currently they're around $16. They're about on par with the Zaffiro.