For my next campaign (hopefully starting up this summer), I intend to use the following core classes from the PH:
Bard (3.5)
Cleric (3.0)
Fighter (3.0 with slight modification)
Rogue (3.0)
Sorcerer (3.0, with slight modifications)
Wizard (3.0, debating various modifications with myself)
And the following core classes from outside sources:
Shaman (Green Ronin) (with slight modification)
Holy/Unholy Warrior (Green Ronin) (with slight modification)
And the following homebrew classes:
Aristocrat (not the NPC class)
Explorer
Expert (not the DMG class)
Fanatic
Hunter
With the following core classes being debated with myself:
Feyborn (Homebrew, but can't smtih rules that really satisfy me yet)
Akashic (Malhavoc Press, fits one of my homebrew races really well but don't want to buy the book just for that one class)
Gutter Mage (Malhavor Press, fits into the slot of 'thief/magic-user' that I've found so hard to do right in 3rd edition, but ditto above. Also, I'm worried about how narrow it is, and might simply convert the class lock stock and barrel into some feats and spells)
I would not allow any core class that I hadn't thought over a good deal, and I don't allow prestige classes. I do however have alot of homebrew feats and tweaks that are designed to allow players to play anything that want with the small set of classes I have, and basically my goal is to move towards having everything in terms of a few highly broad and flexible class concepts. Adding new classes to the campaign without good reason takes away from my goal of having the class system virtually transparent because the classes don't by and large force a particular interpretation on the personality or background of the character. As such, I tend to only like classes that let me generalize a whole range of ideas, rather than classes which seem to have been created to represent one idea only.