The C-64 has the great advantage of having both a TV and an audio/video jack. The latter provides a good picture on a monitor, especially when using a chroma/luma cable. The AV jack also offers a SID input (max. 0.6V).
[ Help! What is the pinout of the 5-pin DIN connector of the original C64 board version? ]
ASCII version:
_______
/ \
/ 8 7 \
| 3 6 1 |
| 5 4 |
\ 2 /
\_______/
Pin| Signal
---+-----------------------
1 | LUMINANCE
2 | GND
3 | AUDIO OUT
4 | VIDEO OUT (composite)
5 | AUDIO IN
6 | CHROMINANCE
7 | NC
8 | NC
Note: All pictures show the plug side.