Cro-moly: this is steel with a high chrome and Molybdenum content for increased strength-to-weight and ride quality properties over standard hi-tensile/hi-carbon steel. Cro-Moly is found on mid-to-higher end bike frames. A variation of Cro-Moly is Manganese-Molybdenum (such as Reynolds 531, etc).
ZR9000 is a trade name (by Trek?) for aluminum alloy containing Zirconium (for the usual reasons...strength/weight/durability etc)
Easton Ultralight: another trade name for proprietary aluminum-alloy frames made by Easton.
Scandium Scandium is a rare-earth mineral and another formulation of aluminum-alloy. It helps stabilize the inherent brittleness of aluminum.
forged alloy forging refers to the method of manufacture allowing higher strength and less stress in alloy parts (like aluminum cranksets, handlebar stems, seatposts, brake calipers, and so on).
6061, 7005, etc this refers to the metallurgical grade of aluminum.
Nowadays, many bikes are made of a combination of materials such as aluminum main triangles with carbon fibre forks and rear end (seat and chain stays).
Hope this helps a little!