Excluding particular source from Get-Eventlog is pretty easy, many of you would have found it. All you need to pipe the output and pass it to where clause to exclude particular sources.
Get-EventLog -ComputerName servername -LogName System -EntryType Error -Newest 100 | where {!(($_.Source -eq 'DCOM') -or ($_.Source -eq 'TermDD'))} | Select-Object EventID, MachineName, EntryType, Message, Source, TimeGenerated, TimeWritten, UserName | ConvertTo-Html | Out-String
The above script will exclude DCOM and TermDD source from the logs and displays EventID, MachineName, EntryType, Message, Source, TimeGenerated, TimeWritten, UserName