The setting for what I'm planning to create these core classes for is more a futuristic setting, with little or no magic. The basic classes, as I have them in mind, sorta reflect the four main core classes from 2nd edition to a certain degree (warrior, doctor, and spy types, basically, but I'm also putting together a class with leadership qualities, sorta like the paladin... might toss it in favor of the base three I listed above and just make the leadership qualities similar to feats). I want to make them unique, yet also completely balanced. The problem is figuring out how exactly to do it, since what little of the class-building stuff I've seen deals specifically with medieval settings, and the DMG isn't too helpful with anything other than stats for futuristic weapons (unless I royally missed something in the books).
I do, however, want to avoid as much of the min/maxing problems that crop up in some of the core classes (most notoriously in the cleric, if the words of quite a few of the WOTC forum members are to be believed). Hence, my job will likely be that much harder. My focus is more on wishing to create classes that have their own unique strengths, yet don't really outperform any of the other classes, but rather compliment what might be perceived as 'weaknesses' with their own strengths (gods, I hope that made sense).