I have a conference room at work and we are adding a secondary display.  I just ordered a Samsung UN55H6203 which is listed on Samsung's website as having one but it arrived with no such thing.  Trying to be in the 55" - 65" range and have a budget of a $1000 max.

Samsung's have the "Exlink" which looks like a head phone (3.5mm) jack in the back. Some genius dug into the service manual of a hospitality grade Samsung that happened to have the same connection, and your modern RS232 driven samsung has been all over these forums since. It's intermittent as hell. I'm 50-50 on getting it to work. It's useless, as it is one way, so if you HAVE to, IR is a better route. Assuming your TV has exlink, which I didn't bother looking up, then you have a chance at rs232, though I don't know why you would use it.If you HAVE to have rs232 than an LG is your best bet. Most of their models have the full db9 connector on back. Everyone else is moving away from it. you might have some luck with Sharps, depending on what series you get. Personally, I wouldn't touch anything out side of sony, lg, samsung, or Sharp just generally speaking.

Thank you so much for your reply.  The Samsung has already been returned.  The 9 pin is a must. We currenty have a Crestron system in place and just need the screen for the back part of the conference room.  The front of the room has and 80" sharp with serial control. The back screen is already wired to match.  We just need the screen for the guy to finish the programming.

Sony XBR models have serial control and they have 55" and 65" models...

Many of the new LG TVs have RS232 ports and the protocol is much easier to deal with than with the Samsung ExLink port.