Background Process that you can Kill

Archivers (ARCn) are my favorite targets. You can solve all kinds of problems by killing the archivers and letting them be automatically restarted. Often issues with redo transport services (Streams, CDC, Logical Data Guard) can be solved by forcing the archivers to restart.

Another time you might want to kill a background process is if it is leaking memory.
Unfortunately, there are many processes in Oracle that cannot be killed. Off the top of your head you might mention PMON, SMON andLGWR. Following are the results from Oracle 11g:

Killable:ARCn: Redo log archivers
CJQn: Job scheduler coordinator
Dnnn: Dispatchers
DIA0: Diagnosibility process 0
DIAG: Diagnosibility coordinator
FDBA: Flashback data archiver process
Jnnn: Job scheduler processes
MMNL: Manageability Monitor Process 2
MMON: Manageability Monitor Process
PING: Interconnect latency measurement
Qnnn: Queue cleanup processes
QMNC: Queue coordinator
RECO: Distributed recovery process
Snnn: Shared servers
SMCO: Space management coordinator
Wnnn: Space management processes

Instance-Critical:ACMS: Atomic controlfile to memory server
CKPT: Checkpoint
DBRM: Resource manager process
DBWn: Database writer processes
LGWR: Redo log writer
LMDn: Global enqueue service daemons
LMON: Global enqueue service monitor
MMAN: Memory manager
PMON: Process monitor
PSPn: Process spawners
RMSn: RAC management server
RVWR: Recovery writer
SMON: System monitor process
VKTM: Virtual keeper of time process