Sorry, I just need to get this out of my system. Too many people still piss and moan about the death of their pure little slum hooker... erm... flowergirl. Let me put it this way, if she didn't die, the planet would go KABLOOIE.
The story wouldn't WORK if Aeris was alive at the end! Why not? I'll tell you why. Holy and the Lifestream. Aeris couldn't cast Holy while she was alive. If it was theat simple, she would have known what her materia did! She thought it was broken, so obviously while alive she couldn't use it. Also, it's very obvious that she orchestrated the lifestream's final blocking of meteor. If she hadn't been in the grave to do these things, Meteor would have blasted right into The Planet whether Sephiroth was alive or not!
Are you SURE you want to bring her back? Yeah, granted Her and Cloud might shag or something, but is that REALLY worth the end of the world?
On an artistic note, Hironobu Sakaguchi would never EVER make her revivable. The theme of the game is life, and to explore the theme of life one must explore the theme of mortality, hence death. Life eternal is not life on this world, by making such an absolute death reversable, the theme of life and mortality is replaced by one of worldly immortality, in the place of a higher ascension. Granted one may say, well, themes can be changed... I seriously doubt that is something Hironobu Sakaguchi would EVER change. The fact that theme is life was brought along by the death of his mother during the production of Final Fantasy 6. Seven was his artistic expression of the pain of his loss.
Aeris' death was absolutely pivotal to the coherence of the story, and for there to be any ending besides the world getting destroyed by meteor... although I personally think they should have played that ending if Sephiroth beat you in the final battles.

-Contra-
PS. Sorry if this is a little random and ranty, I really needed to vent is all. I've had it up to here *makes a here* with people wanting to bring Aeris back...
[Edit] Typos...
[Edit2] Changed the title.