1) Sing closer to the mic - take advantage of proximity effect (Note: assuming your mic is directional)
2) Stop using mics that hype your high end. That eliminates about 99% of the Chinese manufactured condensers. Try ribbons or large diaphragm dynamics if you can (like some of the Heil products, or an RE20). You might also try an SM7, which acts a lot like a large diaphragm dynamic. Do not use Neodymium dynamics, like the RE27.
3) Experiment with multi-band compression in the mix - try squashing some of the offending frequencies.
4) Make sure you are recording in a big enough room that you are not experiencing comb filtering from early reflections off of walls or ceiings that are too close to the mic.
5) If you are adding reverb or delay, try rolling off the high end on the effects.
6) A fattening technique: If the style of music allows it, try doubling your vocals by singing an identical track while listening to the original vocal. Obviously if you are doing classical or jazz, this would be usually inappropriate.
