SQL Server Alerts - Best Practices

What SQL Server Alerts do you always setup for every database? What do you always monitor regardless of the database?

From stackoverflow

• You should monitor and be alerted for severity levels 17 to 25.
  

  Severity levels from 17 through 19 will require intervention from a DBA, they're not as serious as 20-25 but the DBA needs to be alerted.
  17 Insufficient Resources
  18 Nonfatal Internal Error Detected
  19 Error in Resource
  
  
  These are serious errors that will mean SQL Server is no longer working
  20 SQL Error in Current Process
  21 SQL Fatal Error in Database dbid Processes
  22 SQL Fatal Error Table Integrity Suspect
  23 SQL Fatal Error: Database Integrity Suspect
  24,25 Hardware Error
  

  for more information on the severity levels see http://msdn.microsoft.com/en-us/library/aa937483(SQL.80).aspx