Here a few things that Red Ear Sliders seem to enjoy:

Live feeder fish: Guppies, Rosy Reds, and Comet Goldfish all make a great snack and chasing the fish around the tank is good exercise for the turtles.

Chicken, Turkey, and Tuna: These are all favorites, but should not be used often because the high protein content can cause problems with shell growth. Basically, turtles will grow big very quickly with a high protein diet and the growth rate is just too unnatural. Do not give any of these in the uncooked form. Uncooked meat carries Salmonella and can cause your turtle to also carry Salmonella.

Fresh plants and veggies: mustard greens, romaine lettuce, peas, grapes, apple peals, and aquatic plants from the pet shop are all good things to use.
A varied diet is best, no more than 1/2 of all food should be from any one source. Also, diets change as turtles get older. Younger turtles tend to favor meat and are generally more carnivorous. However, as they age, turtles lean more toward the vegetarian side.

Feeding can be daily for little turtles and less frequently (maybe 5 out of 7 days) for bigger turtles.

Habitat: Sluggush rivers, shallow streams, swamps, ponds, and lakes with soft bottoms and dense vegetation.

Diet: Young sliders are carniverous. They eat insects, molluscs and tadpoles. With age, preferences move toward vegetation.

Loves to bask in sunlight, often stacked on top of one another.