More often then not a celebrity chef, that is an actual chef, has come by their status through hard work, creativity and an intense love of food. Chances are their food is better the less they are on TV. But this is not always the case. Chefs like Morimoto, the Arzaks, Eric Ripert, Thomas Keller, Mario Batali and Marco Pierre White have earned every bit of their celebrity status. If you are fortunate enough to go to one of their restaurants you will know why. If you can't, then invest some money in a cookbook and try out their recipes. Either way you will discover why they have earned their reputations.
Another good indicator, now, is the Food Network. Seemingly more and more of it's talent are amateur cooks, for whatever reason they have gotten rid of and stopped looking for truly talented chefs. At its current state I would say the Food Network has more of a penitent to show overrated hype then quality, they have gotten rid of Batali, turned Bobby Flay into a joke and turned their back on Emeril, all the while promoting a veritable who cares of culinary blandness. If you are looking for overrated hype, look no further then The Food Network.
Here are some chefs whose food I've eaten, cookbooks I've tried or general TV presence I've admired:
Jamie Oliver: I received his cookbook Cooking with Jamie from a friend for Christmas. The pasta and main courses I feel are lacking, but the salads, sides and desserts are fantastic. Also any chef that Mario Batali and Anthony Bourdain talk to in a kitchen has to be good.
Mario Batali: He's Mario Batali, enough said. Molto Mario is one of the greatest cooking programs of all time. I own several of his cookbooks and every recipe is fantastic. I've also eaten at one of his restaurants, equally amazing.
Marco Pierre White: 3 Michelin stars at 33 and upon retirement he returned them. He yelled at Gordon Ramsey to the point Ramsey broke down and cried. The man should not be messed with.
The Arzaks: As anyone interested or involved in western gastronomy will tell you, Spain is the place to go. Ask where to go in Spain and they will say San Sebastian and to east at Arzak. He is that good.
There are plenty of other chefs out there that are fantastic. To lump them in with Sandra Lee's and Rachel Ray's of the world is a terrible disservice. The best suggestion I can give is to follow a chef, a real chef, you truly admire and find out who they like. They won't steer you wrong. Above all avoid The Food Network whenever possible.