CAZ is a combat-centered Zoids RP (over your choice of AIM or messageboard) with a judged battle system. Set some time after /Zero.
Generation Zi is a more story-based Zoids RPG with less emphasis on battling. Set in a CC-centric era with organoids and such.- Phenotype's Zoids forums
The site attached now gone, Pheno’s Zoids forums are still going. A bit quieter, but still going. - We Are Zoiders!!
We Are Zoiders is a Korean Zoids discussion forum. - ZoidFans
The oldest English-speaking model fan group out there, now back on Yahoo. Not the most active, but not likely to disappear. 
Zoids Evolution is back, complete with properly hosted forums and general Zoids content. It’s pretty slow these days, but still around!- Zoids Philippines
Another one where the title says it all, though the forum is open to Zoiders from anywhere! 
Zoids Town is a Japanese site including discussion forums and Q+A boards along with news.
Zoids.fr is a French site with information on loakland’s collection, complete with things like country of manufacture (which can make a big difference in batch when it comes to the OER) and pictoral reviews/overviews Also has a forum!.- ZoidsOn BBS
(Non-English) discussion of Zoids, including scans and info on new releases. - Zoidspoison
Hosts one of the more active (English-speaking) forums. Sometimes runs contests. A pretty good source of info on new and upcoming releases, too.