http://otn.oracle.com/oramag/oracle/03-may/o33asktom.html

...Moving on to the core database itself, here is a short list of new Oracle9i features:


Compressed tables. Very impressive. Potentially huge savings.
List partitioning.
External tables. Parallel direct path loader in SQL. I love this feature for data warehousing.
MERGE command, multitable inserts.
Direct path loads with SQL functions.
Program Global Area (PGA) aggregate target. No more sort area size, hash area size, or this size or that size.
Pipelined functions.
WITH clause in select. This reduces the number of times a subquery or inline view has to be materialized to process a query.
User-defined aggregates. Very fast.
Natively compiled PL/SQL. PL/SQL is turned into object code and executed natively in the operating system.
Associative arrays for doing lookups/scrubbing. PL/SQL table types where the index is a string. So, for example, state_name := state_lookup( 'AK' ); would be valid and fast.
Oracle9i Real Application Clusters (RAC). Use Oracle9i RAC if you are serious about availability and scaling out by adding more computers to your cluster as well as scaling up by buying larger computers to replace the smaller ones.
Online operations for everything. Do online rebuilds and reorgs.
Block-level recovery. Use when a single 16K block in a 32GB data file goes "bad" and you need the database to be up.
Significant enhancements to the Resource Manager. Determine the n-active users in a group; make predicative query execution time estimation.
Bitmap join indexes.
Bitmap indexes on index-organized tables (IOTs).
Multiblock size databases. Transport that 4K block size online transaction processing (OLTP) set of already formatted and indexed tables to your data warehouse and do the extraction, transformation, and loading (ETL) using create table as select or insert /*+ append */ with complex queries against the OLTP data. (Your data warehouse will have a 16 or 32K block size, and your OLTP will have a 2, 4, or 8K block size, so this is relevant.)
Fine-grained auditing. Efficiently and effectively capture the questions people are asking, along with binds. This is good not only for auditing, but also for performance analysis.
Resumable space allocation. If you are using Oracle9i, for example, to rebuild a 15GB bitmap index, and you get a space-related error, you can suspend the statement, fix the space problem (add a file to temp, for example) and have the index rebuild pick up where it left off.
Index monitoring. Does anyone really use that index?
Update of GLOBAL indexes. Instead of having GLOBAL indexes becoming invalid and needing to be rebuilt, they are maintained during partition management.
Resize the SGA online. Add block buffers and take them away.
Buffer cache/shared pool/etc. advisors. New V$ tables tell you, for example, that if you increased the buffer cache by this much, you would get n percent more logical IOs