Cartoon Network (ended 2003)
I've seen the ending today - so I am blissed. 
In no way I can see a possible second season. Simply, they lived happily ever after, the "ordinary" peaceful life has come for them after all they'd gone through.
Any further story would be a simple soap opera of their lives and them organising the new order. Wonder if there's any other humanity left? What would happen to all those reckless soldiers on Earth met on previous episodes and nomadic people?
Would there be a different enemy? I feel it would be very artificial then...
There are a lot of questions, but in the end, I don't feel like I want to know answers. It's like giving the heroes a little privacy ... or like giving yourself the opportunity to fantasize for yourself! 
@Aleven: Well said, I agree with you completely. In fact, Blue Gender was one of the few anime series that didn't leave a bitter taste in my mouth. Most of the time it seems animes go for one of two things: the tragic ending in which the protagonist dies, or the bittersweet ending where the central conflict is resolved and things just return to the way things were/everyone involved decides to go their separate ways (lookin' at you Samurai Champloo). Finally, there's the rush-job ending where the show a) catches up with the manga it's based on and ends abruptly, or b) in a straight-to-anime release, the plot falls apart at the last minute, souring what could have been an anime classic, leaving you absolutely clueless as to what you've just witnessed (Evangelion, anyone?) or c) uncertain whether the show will be cancelled, the series planners write in the possibility of a second season but never follow up on it (Outlaw Star, we hardly knew ye). None of these scenarios is in evidence here, and I'm tempted to say this is one of my favorite animes of all time in terms of plot, character development, action, and animation. A thoughtful, satisfying conclusion is icing on the cake for a show of Blue Gender's caliber. In all honesty: what more can one ask for?
