You can indeed sharpen most twist drill bits, and doing so not only keeps the bits more effective, it also increases the safety of your drill, as dull drill bits are more likely to slip or skid across hard materials.  There are electric drill-bit sharpeners available that make quick work of restoring the point to your twist bits. You can also tackle the job yourself with a bench grinder or a rotary tool with the appropriate grinding attachment. Another option is to use a metal sharpening file to do the job by hand.