Looks like the in-game server listings are not working properly today. I'm getting either no listing or a short partial listing.
My monitoring shows that there may be a network problem affecting the Master Server (which provides the listings).
I've notified Bungie to request they look into it (since they host the Master Server). I'll update this if I hear anything back before it gets fixed.
In the meantime you can still connect to Halo servers by Direct IP in Halo, or through Xfire. Our server listings are HERE.