I play on the www.diplom.org, which has also a nice zine with a lot of interesting articles. (And gorgeous .ps-maps)
Perhaps we should organize a Hacker game once? Even if we can't find seven diplomats (+ a GM), there are interesting variants for a smaller number of players. Like `Hundred' or `Sail Ho!'.
Ido, what do you think of this article: [http://www.diplom.org/Zine/F1997R/Windsor/lawdip.html]?
I think it's too long for me to read at the moment ;)
For a lot of the web based ones (including the site I mentioned) you do not need a GM, it is arbitrated by the computer.
It also works a lot quicker and is more user friendly than PBEM.
I play in communities where computer arbitration is the norm. Still they require a GM (and I think rightly so) to guide the game, search for replacements and answer questions. (And it is still technically PBEM, because the server uses email as the primary interface.)
However the typical workload for a GM is far lower than without computer arbitration, of course. And you can read all the negotiations, if you want to.
The communities are generally pretty small.
My experience in playdiplomacy.com is that it doesn't feel like a bunch of strangers after a couple of games, especially if you go to the forums - since playing diplomacy (with good players) normally involves quite a lot of talking, you can make somewhat more significant ties than in other online games.