Warrior Cats: The Four Clans

Zoids are, I believe they called them, biomechanical monsters that take the form of any animal, real or not.
There were five season (Chaotic Century, Guardian Force, New Century Zero, Fuzors, and Genesis). You could watch them in any order with the exception of Chaotic Century and Guardian force. GF makes no sense if you don't watch CC first. You won't know anyone and you won't know why there's tiny black dragon Zoid stalking a crazy kid who's on a rampage and doesn't seem to know what he's doing (He actually does know what he's doing).
Every season after that gets a new set of characters and very hard to spot things that ties that season to the previous season. Some you'll never notice unless someone tells you or you read about it somewhere else.
Here's a neat video that gives you a better idea of what ZOids are like. (No, the color isn't really like that for the show, its an effect added by the creator of the video who makes amazing Zoid videos. Do not watch any others unless you want to spoil parts of every season.)
http://www.youtube.com/watch?v=9vlAbeDF9AM
I'm going to see if I can name all the Zoids shown in the video in order. I won't repeat any though.
Mugen Liger, Murasame Liger, Hayate Liger, Liger Zero! He was there! very briefly.... Bio Raptor, also very short appearance. XD Bio Kentro I think is what that one is called. Panzer! JAger. Volcano. Those crazy parts are hard.... Zaber Fang! Didn't actually know that scene was int ehre. And no, I will not tell you what scene it was. Blade LIger and Stealth Viper. Elephander! And you can barely see a Command Wolf. Godos? I forget its name... XD Shield Liger! I saw you Schneider! Lance Stag. Hey! I didn't know Berserk Fury showed up this early in the video. XD Looks like Death Saurer makes a breif appearance as well. Storm Sworders. So awesome. Shadow Fox! Gun Sniper! genosaurer! Boom goes the Ultrasaurus! He stole the Jurassic Park theme.  Bio tyranno! If you have decent eyesight, you may have seen Soul Tiger. He's not actually that hard to spot. That is definitely Deadly Kong. There you are Bunny Liger! (No, that is not a real Zoid, its a nickname.) Zero Phoenix. (Zero, you have way too many forms.) STOLLER! (Not a Zoid or nickname.) Lightning saix. War Shark. Was that a Zabat? I saw Gairyuki's lasers, but no Gairyuki. Dark Horn and Deibison. Thomas, stop hurting yourself.  By now you should be at a scene were A zoid brutally kills another (I won't tell you tehir names XD). that is not blood. When a Bio Zoid dies, gold an red sparks shoot out form the wound and then armor dissolves. Sparks, not blood. I think I may have saw genobreaker! Revraptor. A few Gordos (Their name is actually Godos, but the dub changed it to Gordos for some odd reason.) Stop being mean Raven. Sword Wolf! Mega Bio raptor.  Was that a red Horn? I saw Attack cat/ Hellcat!
dang, that was tough. No, that is not all the Zoids. that's jsut a few of them. XD
If you want to watch teh show, PM me and I'll send you the link. The episodes were hard to find and you won't be able to find them on youtube. Spanish epidoes, yes, english, no. 5th season is subbed only. All the the others are dubbed only.