My last entry on connector sparked some discussions in the altpwr telegram, and I've done a bit more research and thinking since, so I'd like to share some more connector options.

• IEC 60309
  
  Commonly known as CEE plugs, this standard has an option for low-voltage DC as well, mostly white 2/3 pin plugs. From my understanding, for 48V we would need a white casing with the keying at 10h, which are available in 16A and 32A. They seem to be a little hard to come by, but PCE has them in their product catalog, and Conrad seems to carry them. As with the other plugs from the IEC 60309, they are probably pretty study and weatherresistent.
• RJ45
  RJ45 is everywhere, and most of us probably have a few meters of networking cable lying around. Given that and the existence of Power-over-Ethernet might make this a decent candidate. There's a bunch of cheap adapters for so-called passive PoE, which is essentially just 12V or 24V across the two unused pin pairs when running 100Mbit Ethernet across a standard ethernet cable. Given the size of the connector pins, you're not going to move much current across these connectors.
• Weipu SP21
  A type of connector that came up in discussions at 36C3 and in the altpwr group. There's a 5pin version with 2 large power pins, and three smaller pins that could be used for communications.