My personal faves are, Deli-News, Crossroad's Diner,
Smoke, and Hattie's.
Smoke and Hattie's are in nearby Oak Cliff. Deli-News is in North Dallas and Crossroad's Diner is on Walnut Hill east of Central Expy and west of Greenville Ave.
However, there are probably over a hundred good brunches
to be had in Dallas and I'm sure others will tell you their favorites.