In the Rock Hill area:
Mary's Cafe located at 101 Porter Road has good food. A local Mom & Pop restaurant.
Varsity Restaurant 108 Oakland Ave owned by a retired RH policeman another good Mom & Pop. It's near Winthrop University.
Red's Grill 1101 East Main St been here forever locally owned and great food.
Ebenezer Grill 1525 Ebenezer Rd. locally owned ... offering sandwiches ... famous for their Hot Dog Sign that was stolen last year. Great soup and sandwiches. Been around forever too!
Thursdays Too 147 Herlong Ave. Locally owned by the Bigham family and everything is good.
White Horse Ltd. 1022 Camden Ave located near Winthrop University and excellent food.
Nishie G's Cafe 706 Mt. Gallant Rd. Greek cuisine delicious dining and locally owned.
In
Lake Wylie my very favorite is:
The River Rat 5301 Hwy 557 Lake Wylie ... it's been around forever, the Powells own The Rat and everything and I do mean everything is wonderful to the taste buds.

They have a website: The River Rat Restaurant & Pub (broken link)
Sonny's Dutch Mill in Rock Hill,
Steve's Fish Camp,
York Seafood have all been mentioned already and they do have good food.