What APIs and endpoints are available for working with Windows Event Logs?
What APS's are new/different in Windows Vista and newer?
LogParser: Has a COM API as well as a command line application. Recommended. Also reads many other types of logs.
WMI: Can be made to read event logs. Doesn't perform well.
Windows API: If you are programming in C this is the way to go.
C#: Managed APIs exist also.
See the microsoft Windows Event Log API here:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa385785(v=vs.85).aspx