One option is to buy a Drill Doctor. These range from $50 for your Basic Drill Doctorto their $150 Professional Drill Bit Sharpener.
Here's an article on How to Sharpen Twist Drill Bits.
The article shows you how to freehand-sharpen a twist drill bits using a grinding wheel. While it's not too difficult, there are several important things one must know and do. In addition to learning the correct angles, the article explains the three distinct motions one must use while holding the bit against the grinding wheel.
1 - Move the bit to the left (grinding on the left edge only)
2 - Rotate the bit in clockwise rotation
3 - Move the bit downward
Read the full article on Resharpening drill bits, courtesy of Woodcraft woodworking stores.