Green aliens, dog robots and paranoid paranormal investigators...

An excellent, if somewhat sick and twisted cartoon created by Jhonen Vasquez for the Nickelodeon cable channel. Jhonen's sense of style and writing seems to have come through faithfully and without too much censorship. His friend Roman Dirge of Lenore fame has shown up in the writing credits as well. For everyone wondering how the creator of JTHM got a Nick show, he was asked by a Nickelodeon executive named Mary Harrington who enjoyed Squee. As you can imagine, Jhonen is somewhat unhappy with the management and forced collaboration that comes with a TV show, but he's managed to stick with it.

Main characters:
Zim - Richard Horvitz - Our little green alien, the incompetent Irken invader of Earth
GIR - Rosearik Rikki Simons - Zim's annoying broken robot, oft disguised as a dog
Dib - Andy Berman - UFO fanatic and the only who realizes the truth about Zim
Gaz - Melissa Fahn - Dib's gothy video game obsessed sister

Supporting characters:
Mrs. Bitters - Lucille Bliss - Zim and Dib's nihilistic old viper of a teacher.
Allmighty Tallest Red and Blue - Kevin Mcdonald and Wally Wingert - The Irken leaders who sent Zim to Earth by accident in the first place in an attempt to get rid of him.

Zim's RoboParents - Zim's robotic parental figures. They were educated in the ways of normal Earth parents by GIR. Oops.

Season One:
1. The Nightmare Begins - Zim's little slipup before an invasion ends up with his banishment and eventual exile to Earth under the guise of softenining it up for conquest. He arrives and meets Dib in school, leading to conflict between the Invader and investigator.
2a. Parent Teacher Night - Zim's robotic parentoid come to school after being tutored by GIR, and there's a few problems...
2b. Walk of Doom - Zim tests GIR's fixed directional chip by taking a walk. Of course, GIR leaves it behind, and Zim tries to find a non-lethal way home.
3a. Bestest Friend - Zim seeks companionship to avoid being found out and put on an autopsy table. Too bad he picks a rather Fatal Attraction-like friend, but Zim knows how to deal with it.
3b. Nanozim - Zim is ambushed at home by Gib for photo proof of his inhumanity, and resorts to a rather fantastic way to dispose of the evidence. Gaz helps, inadvertently.
4a. Germs - Zim catches a War of the Worlds ripoff on the tube, and becomes germphobic after having its message of doom verified by the Irken internet. GIR is as helpful as always.
4b. Dark Harvest - When Zim gets sent to the nurse, he needs to borrow some human organs from the school children to hide his species. Eeew.
5a. Attack of the Saucer Morons - Zim has a run in with UFO fanatics who capture his ship and expose him as an alien. Uh oh. They start worshipping him. Even worse. Best episode ever.
5b. The Wettening - Irkens apparently don't deal well with rain or water in general, and Dib takes full advantage of this until something goes horribly wrong.
6a. Career Day - Blot tests lead to suggested employment choices, and while Dib's happy with his job at first, Zim's fast food career gets unpleasantly interrupted by cosmic forces.
6b. Battle Dib - Dib is invited to describe his findings on Zim to a group of fellow fanatics, but the signed parental permission slip it requires will put him straight in the path of Gaz as he attempts to get into his father's TV show.
7a. A Room With A Moose - Zim attempts to rocket bus his many tormentors to another universe - should Dib bother to save them, even if it means his own death?
7b. Hamstergeddon - Ms. Bitters brings in a pet, and Zim gets an idea from the human reaction to cuteness. Ever see Godzilla?
8a. Invasion of the Idiot Dog Brain - Gir is trapped in the house's computer system. He decides to get himself a Taco and takes the house out for a night on the town.*
8b. Bad, Bad Rubber Piggy - Zim tampers with time, replacing items from Dib's past with rubber piggies. Dib is nearly killed... nearly.*
9a. Planet Jackers - Earth is finally set to be destroyed- but not by Zim. He wants to save the destruction for himselfit for himself.*
9b. The Rise of Zitboy - Zim's hypnotic pimple allows him to rule the playground.*
10a. Plague of Babies - Zim is seen out of disguise by a baby. Babys can't talk, though... Or can they?*
10b. Bloaty's Pizza Hog - Gaz just wants supper with her family at Bloaty's. She goes to great lengths to get her brother there on time.*
11a. Bolognius Maximus - Dib is injected with bologna DNA and slowly turns into lunchmeat. He's able to exact revenge, however- but it's too late.*
11b. Game Slave 2 - Gaz really wants the latest, greatest video game system. But Iggins wants it too.*
12. Halloween Spectacular of Spooky Doom - Dib is trapped inside his own giant head.*

Season Two:
13a. Door to Door - Zim and Gir compete for the top prize in a door-to-door selling contest.*
13b. FBI Warning - Gir rents a video and Zim is spooked by the standard FBI Warning. He breaks into the mall to return the video, but he must get past the security guard.*
* = anotherone wrote it

The official Invader Zim site is at - warning, requires a Flash plugin.