Just go with something that includes Halo. I mean.. unless you sell something and make a lot of profit under name "Halo" I highly doubt there will be any trouble. Especially if you're just going to make a community, or regular fan-site.

I personally haven't heard of any case that someone has been sued for using something like "HaloWarsCentral" or "Gta-sanandreas" or whatever game name for fan site. In the end Halo would probably even sell some more copies because of that site..

I don't think any game company would be that stupid to shut down some community just because it uses some game name in its domain or whatever. Company would probably get a lot of bad rep. sell less in the future for that..