You're right -- my lo-tek campaign needs a matrix of classes with specializations, and really ought to be compatible with CT chargen. So I'd say six to twelve classes, generally falling along traditional caste lines, and a skill chosen as a specialization within that class, perhaps from a list tailored to that class.
Of course, Shriekers have a caste system of sorts, and in fact have a list of specialization skills [i.e. primary skills] for the classes.
So, assuming four basic classes:
Serf
Warrior
Seeker
Priest
And specialization skills from which to select Primary and Secondary Specializations (say 12 available per culture from which to pick specializations):
Athletics
Awareness
Carousing
Chameleon
Craft
Dodge
Farming
Healer (Medic)
Hibernate
Hunting
Law
Leader
Long-range communication
Mathematics
Melee (Lone combat)
Memory
Perception
Philosophy
Poetry
Ride
Sail
Stealth
Survival
Teacher
Teamster
Trader
Weapon combat
...yields over 500 different character types, including the old standbys (Warrior + Healer + Philosophy = Paladin; Warrior + Melee + Philosophy = Ninja; Warrior + Healer + Hunter = Ranger...) as well as all the character mixes from Adventure 10. Rich soil for players.
Plus, of course, Elder versions of all the above (which is part of the aging process).
And, if that isn't enough, I've attempted an adaptation of psionics to fit supernatural settings here:
http://home.comcast.net/~downport/rules/variants/jumpspace-gods.html