First, I suggest using KBB.com to help you, they have a lot of information as well as what you should be paying based on your area (comes in handy with used dealerships/private owners), it can show you how much a car can cost you over the years with its maintenance and insurance included with price of that specific car. you can also find good reviews at MotorTrend.com
Second, if you want luxury or sporty. More and more sporty or "power-house" cars are starting to take on a luxury look. However, the luxury cars nowadays are unbelievably amazing and come with some pretty neat features. As olyteddy said, definitely buy, I suggest avoiding most 1st year and some 2nd year cars of a generation, they typically have more issues than the years to follow of that same generation. A cars value practically cuts in half after two years also, usually being certified as well, depending who you get from, they can have pretty decent warranties too.
If you want sporty and like the Ford Mustang, I suggest looking into the Dodge Challenger and Chevy Camaro as well. The newest generation of Dodge Chargers (which I love) have improved in looks but it is in its first year of the new generation (yet the car wasn't drastically changed, just its looks.) While the 1st three cars were just two door the charger is a four door. My opinion though, these cars aren't worth anything unless they're a V8, which will come with the gas guzzler tax...
Lexus's are nice and expensive too. I was talking to my mechanic one day and he mentioned he was replacing a "liquid-cooled" alternator, that was $1000 for just parts. I don't remember the actual model I'm hoping it was high on the list. BMW's M series will turn a lot of heads. One down fall, Lexus and BMW aren't well known for great warranties.
If you like trucks, the Lincoln Mark LT's is my favorite truck. For a cheaper route Ford/Chevy are good choices
If you like SUV's, GMC has the Yukon, Envoy(no longer in production), Terrain, and Arcadia. The Yukon, Envoy, and Arcadia have the Denali package option, which is for the spoiled If anything the Envoy or Terrain would suit best out of the four unless you're needing more than 4/5 seats.
Last but definitely not least, Hyundai. They have had the best increase in value retention and are topped #1 right now, as well as they have had an increase in quality. The Genesis is pretty nice too, a family member of mine has one. Its exterior is black, with a black and brown interior. I believe they come as coupe or sedan too.