He's already been nominated, but I consider IainPeregrine to be one of the best active developers on BYOND, if not the best.

There are some skilled developers who don't produce finished products (I might fall into this category as the only things I've finished are libraries), but Iain has put out Plunder Gnome, Jeet Kune Do, and---more recently---Regressia, all of which I have enjoyed immensely or plan to, as is the case with Regressia. He puts in the expected amount of polish and makes the games fun.

Another name that I might suggest is Kajika (though he's not active in any social aspect of BYOND). His Duel Monsters Online game functions well and has attracted a consistently large player-base almost 24/7 for years. Back when game rankings were in effect, his Duel Monsters Online was constantly vying with Last Robot Standing for the top seat.

Edit:
Also not to be forgotten is Aaiko, who semi-regularly puts out new games and also produced Seika.
I personally BELIEVE that when Developous was around he was one of the BEST, MOST EXPERIENCED developers. He made a game a day, and it was only because of YOU ALL that he failed, because HIS GAMES were perfect.
Silk Wizard tends to produce polished games.
I can call many people active developers (including myself). However there is one 'but', whenever I start X project, I do login, battle, some other features, then I encounter wall: no iconers and people who don't want to help to test because of lousy icons.

It's a lot more community, than developer problem at the moment, it's WAY easier to get people's interest by ripping and changing name of it, than making something original. No one really want to make anything, if you will have 0 to 3 people playing, and see 50 people online on a game, which is similar to other 20% just different name
Theodis isn't very visible, but he is around and active, especially when someone makes a suggestion about one of his libraries. Programming communities need a strong basis of good libraries dealing with basic data structures and useful algorithms.
In response to IainPeregrine (#24)
Well I don't know if I qualify as being too active. I just lurk around occasionally and do a forum search for my handle and the random patch work to my libraries most of which are 4+ years old now. Though Kuraudo has been trumping some of mine :P!
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