Ask HN: what makes a great community?

I have small community of programmers on Facebook, around 10,000 members spread across various groups and a few pages.

I'd very much like to bring the community to the next level, by way of its own website, with dedicated forums, chat, etc. I'd like to integrate this closely with the FB community so that there is little resistance in migration from one platform to the other.

My own platform gives me more flexibility in how I build and grow the community. I was just wondering what, in your opinions, make for a really good, great even, community?