'''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
All Shimano Tiagra, 105 and Ultegra as well as LX, XT (and anything lower) cassettes are all steel cogs. Dura Ace and XTR do use Ti for their largest cogs but all of the smaller ones are steel.
Campagnolo makes an all-Ti ($$$$) and partial Ti versions of their Record cassettes. All of their other cassettes are all-steel.
The only Aluminum cogs I'm aware of were briefly made in the mid-1980's by Sun Tour in their "Microlite" series of freewheels and Campy also made an all-aluminum freewheel for a brief time. These had extremely poor durability and the weight savings wasn't worth the very low service life.