If your cakes only come out uneven every once in a while, it might be that your cake batter is not mixed thoroughly. Try beating it for another minute or so and try again.
If all of your cakes turn out uneven, your oven may be the problem. Uneven heat may cause cakes to rise haphazardly. Try turning your cakes a few times while they bake to see if this helps.
An oven that is too hot can also cause uneven baking. Use an oven thermometer to check your oven's accuracy. If it is 25 degrees higher than the setting, just lower your baking temperature by 25 degrees. If the temperature is off by more than 25 degrees, have your oven recalibrated.
It's also possible that your oven is not level, and this is causing uneven baking. To check, fill a loaf pan with water, place it on the oven's middle rack, and look to see if the water is even. If not, your range's leveling legs may need to be adjusted.
Try the above champagne cake.