Dreamcast:Video Cables

Unbranded Cables
Most of the unbranded plug-and-play HDMI cables the Dreamcast aren't compatible with any 480i/240p game. Some have a very soft output, and others barely work at all. They don't seem to add lag.

Beharbros Analog to Digital Converters
The Gekko and Akura by Beharbros are analog to digital converters.

Both the Gekko and Akura output 480p over HDMI, and the quality of the image and latency may vary depending on how well the connected display upscales the image to the display's native resolution. All VGA analog to digital converters will not correct the aspect ratio and sampling issues.

Gekko
The Gekko specs includes features 480p output from HDMI, a 15khz RGB/31khz VGA mode switch, and stereo. The manufacture does not guarantee that all non VGA games will work.

Akura
The Akura Analog to Digital Converter offers the all the same features as the Gekko with the added functionality of configurable scanlines.

Component YPbPr

 * RetroGamingCables YPbPr cable (review)

VGA
The Gekko/Akura mentioned above can output VGA. The.Foo83 on ebay occasionally sells custom VGA cables with a 240p/480p switch.

Tomee and Kaico sell comparatively bad quality VGA cables.

SCART

 * RetroAccess RGB SCART cable
 * RetroGamingCables Dreamcast PACKAPUNCH RGB SCART cable

BNC

 * RetroAccess RGB BNC cable