Has anyone ever posted a list of the most popular MoO2 fan sites?

Google

Thanks for the sage advice. That never would have occurred to me.

The sites I've found most useful are:
The Guardian for tech tree and other goodies.
MoO2 Online for tips on multiplayer.
[url=http://strategywiki.org/wiki/Master_of_Orion_II:_Battle_at_Antares]MoO2 Wiki[/url] for general tips and insights.
Gamefaqs some interesting guides.

All found within first 10 hits on Google, so I imagine most people already know about them.

Ill definitely wouldnt recommend Gamefaqs from the Google selection, the only useful FAQ from there is Gontzol Weapon Guide, as its generally correct in most things described, the other ones are misguiding at best. I'd add the http://www.spheriumnorth.com/orion-forum/nfphpbb to the list, thought its technically just the forum connected to http://masteroforion2.blogspot.com/ mentioned. Strategywiki is generally decent in data quality, but somewhat hollow it it still.

Yeah the Gontzol guide is definitely worth a read.

http://lordbrazen.blogspot.ru/

Site of Lord Brazen whose fixpatch is added in GOG MoO2 package.

http://www.orionsector.com/index.php

Debris of long-dead Orion civilization. For space archaeologists only.

http://www.mo3.fatal.ru/index.htm

Russian Orion fan-site, has localization projects, mods and such.