NES - composite video (yellow) and audio.
Some new HDTVs don't have a dedicated composite connection, but they let you connect your yellow composite cable to the green connector from the component video input (green, blue, red connections). Some TVs don't even have component without a little squid cable that goes into a 3.5mm jack.
SNES/N64 support S-video natively. If your TV has that, make sure you get a quality S-video cable. The ones that have a composite video connection (yellow) on the same cable are pretty much all garbage. They just send the regular composite video (chroma+luma) signal to both the chroma and luma pins (the point of S-video is to keep those signals separate).