Metalink says: These are the oracle created schemas used by various features you can drop them if you are not using those features..
Code:
DBSNMP if Enterprise Manager Intelligent Agent is installed 
TRACESVR if Enterprise Manager is installed 
AURORA$ORB$UNAUTHENTICATED \ 
AURORA$JIS$UTILITY$ -- if Oracle Servlet Engine (OSE) is installed 
OSE$HTTP$ADMIN / 
MDSYS if Oracle Spatial option is installed 
ORDSYS if interMedia Audio option is installed 
ORDPLUGINS if interMedia Audio option is installed 
CTXSYS if Oracle Text option is installed 
REPADMIN if Replication Option is installed 
LBACSYS if Oracle Label Security option is installed 
ODM if Oracle Data Mining option is installed 
ODM_MTR idem 
OLAPSYS if OLAP option is installed 
WMSYS if Oracle Workspace Manager script owmctab.plb is 
executed. 
ANONYMOUS if catqm.sql catalog script for SQL XML management 
XDB is executed
Also these sample schemas can be dropped safely..
Code:
HR (Human Resources) 
OE (Order Entry) 
PM (Product Media) 
SH (Sales History) 
QS (Queued Shipping) 
QS_ADM (Administration) 
QS_WS (Western Shipping) 
QS_ES (Eastern Shipping) 
QS_OS (Overseas Shipping) 
QS_CBADM (Customer Billing Administration) 
QS_CB (Customer Billing) 
QS_CS (Customer Service)