I think your best bet would be to get a hold of guys like Darren
Grey, Andrew Doull and Ido Yehieli. Those guys do a lot of the
Roguelike Radio stuff and Doull even has his own developer website.
It's called Ascii Dreams. He runs the Roguelike of the Year on his
blog.
http://roguelikedeveloper.blogspot.com/
And here is a link to roguelike radio. You'll get to hear Grey,
Doull and Yehieli and their sweet accents. I recommend episode 16
where they talk about the history and future of roguelikes.
http://roguelikeradio.blogspot.com/
Another good place for discussion is on Temple of the Roguelike.
It's a bit more active than this google group. A lot of the same
people will post though. Slash maintains it. He also wrote quite a few
roguelikes. I think he runs the 7DRL competition (i think).
www.roguetemple.com
Other than that each roguelike starts to develop it's own fanbase.
When this happens forums dedicated to that roguelike pop up. There is
one for Brogue, Dungeons of Dreadmor and ToME4 that are pretty lively.
I've never checked them out though. I imagine Crawl has a pretty sweet
forum as well.
I do not know how much you play roguelikes but I'd recommend
checking out the original Rogue, maybe a little Nethack and then some
of the newer ones like Brogue, Crawl and ToME4. DoomRL also has a big
community. I'd say check out Dreadmor but you'd have to pay. The rest
are freeware. I'd also say check out Dwarf Fortress but it's only a
Roguelike in the broadest sense.