I think 1 minimum, 500 maximum.

All thats needed in games like EQ2, WoW, VG etc are tank, healer, dps and cc and thats it. Tank to take on the damage, healer to heal the tank, dps to melt faces. CC to mez, aoe freeze, sheep, lul or w/e. Thats all thats needed and there are classes in there which do those specific things and do them the best. But it's nice to have hybribs and jack of all trade types of classes too for those who get bored of doing the one roll all the time. Like WoWs class paladin is either a tank, healer or dps and is capable of all 3. Same with WoWs druid can be tank, healer or dps. Theif type classes usualy are a dps / cc hybrid. VGs bard a jack of all trade. VGs psi cc / dps hybrid usualy pure cc type of char. EQ2s templar tank / healer. So, it's good to mix it up a bit otherwise all your stuck doing is tanking, healing or dpsing. Or in some games cc where required.

Whereas games like UO, Runescape etc don't really need classes as your free to do what you want and take whatever path you want to. In RS you can either be warior, archer or mage or all 3 if you chose or even adventurer (skiller) so no classes are required in those cases as everyone pretty much has the same role with exceptions.

So, it depends what type of game your playing as to what classes are required or even if one is required at all.

I agree with the post above...

indeed.. classes are very needless. without classes the players have much more room for their personal decisions.

 42...the answer is ALWAYS 42

Jokes aside i actually touched this topic in a story i'm wring called "Just a Game" which basicly involves people becoming part of the game world (think .hack). Character creation involved a uh "encouranging" AI and "countless classes" with the decision nailed down not by "ok i choose yooooooooooooooooou" but a sort of question tree 

"spells or sword?"

"want to be tough? Strong? Fast?" and so on.

Not more , not less :

mage ( sorcerer , healer , shaman )
scout ( archer , assassin , trapper )
warrior ( duelist , knight , paladin )
specialist ( crafter , alchemist )
summoner ( necromancer , beast master )

Character classes are ridiculous. Every time a new game comes out with classes, God kills a kitten.

Originally posted by armomotbg

Not more , not less :

mage ( sorcerer , healer , shaman )
scout ( archer , assassin , trapper )
warrior ( duelist , knight , paladin )
specialist ( crafter , alchemist )
summoner ( necromancer , beast master )

there could be more if you put a lot of thought into it after all games should test your imagination