Meanie...... (what exactly is an Invader Zim?)  and GIR? sounds like something you might clean the bath with!!
Tell us more!!

Perhaps that should be a challenge.. a short UFO/crossover  story involving one of the following;
Bonanza,
Charmed
High School Musical
Hannah Montana
The Mentalist
Bewitched
Mr Ed!  Go on...you remember...the talking horse!!

I am only joking ... don't start planning!

If we ever do a crossover challenge a have a great JAG/UFO idea!

I might do it anyway! (Matt looks at his ever growing writer's to do list and add's another story)

My wife would insist that I do Bonanza! Hell she might even read that one!

Look........Who is Invader Zim? and JAG?

I could be really mean and give you a crossover such as ....Telly Tubbies and UFO

Mentalist, Denise? Don't like it? I only watched a few episodes and it was sooooo predictable!
And the main guy has no charisma at all!

Now CSI is okay! .. Horatio Caine? v Ed Straker... I know Amelia has done CSI  crossovers, but I prefer Horatio to Gus Grissom...... perhaps its the sunglasses!

Invader Zim is the Bomb!    He just wants to conquer Earth is all.  Just your regular harmless extra-terrestrial.  Really.  *snicker*

Yeah, the guy on Mentalist is such a loser!  Where did they find this guy?  What a mistake!  He's the star of the show, for godsake!  Isn't he supposed to be at least charming?  Yuck!    And double yuck! 

Pam has CSI:Miami / UFO crossovers.  She doesn't explore much with H and Straker head to head, but the stories are still really good.  She also did a CSI / UFO crossover with Griss, but he didn't meet Straker either.  I'd love to see H and Straker go at it!    Two men with strong principles on opposite sides of the fence -- what's not to love? 

<snerk> The problem is, I love GIR. His answer to why he does things is frequently a little: I ... don't ... know. Straker would crunch GIR. Alec would look at it askance and Dr. Jackson just might enjoy its bent sense of humor. On the other hand, I can see Ford adopting it... this may be why the xover derailed. INvader Zim is a guilty pleasure. Gross, disgusting and totally bent ... lots of fun! I feel sorry for the only character who's figured Zim out (Dib) because no one believes him and  ... Oh, shoot! sudden vision of Zim telling the spinners off, after all, this is HIS planet to conquer or destroy, depending on how he feels about it today! The Tall will not allow the  .... Oh ... no ... LOL         Now I've done it!!!!

<dragon runs screaming from her muse who looks like GIR>

d

Johnny Quest has been done, Helen Weber wrote it. It's in the library, quite a good story!

If you wanted to stay with a serious story you could go with the GI Joe cartoons. 

There was an animated version of Fantastic Voyage that was almost mothing like the movie that would be a good choice for a crossover. The organisation was called CMDF (Combined Miniature Defense Force) and the ship was called Voyager. I only remember the pilots name, Professor Buzby Birdwell (no kidding). The show ran sometime in the mid to late sixties.

I had to dig but I found the rest Johnathan Kidd, Erica Lane and Guru.

On the lighter side there's Keith Ford and Duck Dogers!

Go for it Louise!

But it is fun bouncing around all these good ideas!