Hopefully, you've multiplexed your control files so you have at least one more copy of the control file. Let's assume that you have three control files:
You lost control02.ora. Simply copy any one of the other two files and rename it to replace the missing control file.
Another option is to remove the missing control file from the CONTROL_FILES initialization parameter and start the database. This option only works if you have at least one good control file.
If you only have one control file, then you'll have to start the database in NOMOUNT mode and use the CREATE CONTROLFILE command to be able to create a control file.
One should always multiplex the control file so that recovery from a missing or corrupt control file is as easy as copying from a good control file.
This was first published in March 2006