Oracle 8i DBA Handbook by Kevin Loney & Marlene L. Theriault,
This book is ideal if you are new to database admin - it does duplicate some of the Oracle documentation, but a one volume summary may be just what you need.
about $50 - buy at Amazon.com

Oracle 9i DBA Handbook
The same book updated for Oracle 9i
about $42 - buy at Amazon.com

NEW - Oracle9i Administration and Management by Michael R. Ault
Tons of examples and scripts for Oracle 8i and 9i also includes "How to be hired as a DBA"
about $45 - buy at Amazon

Practical Oracle 8i performance by J L Lewis.
I like this book a lot - many computer books are packed with technical detail - this one is packed with the wisdom of Jonathan's extensive 'practical' experience
about $45 - buy at Amazon.com

Expert One on One: Oracle by Thomas Kyte
Full of examples and useful techniques that demonstrate how to build faster, more scalable applications, from the man behind 'AskTom'
about $42 - buy at Amazon.com

Oracle Desk Reference by Guy Harrison,
A compact guide covering SQL, PL/SQL syntax, built-in packages, API calls, configuration parameters - a good reference to carry around.
about $30 - buy at Amazon.com

Oracle 8i Internal Services: For Waits, Latches, Locks, and Memory by Steve Adams,
Very good, but not for beginners - a lot of advanced theory packed into a small book
about $14 - buy at Amazon.com

Oracle 8i Backup & Recovery by Rama Velpuri et al.
Covers more than just import and export - good introduction to Archive logs, physical and logical backups, replication methods, backup scripts, hot standby databases plus repairing database corruption with the DBMS_REPAIR package
about $45 - buy at Amazon.com