The SharePoint ULS Viewer by Dan Winter, Microsoft - http://archive.msdn.microsoft.com/ULSViewer

If you need, here is a list of SharePoint ULS log viewers out there along with comparison of features and the verdict on which is the best ULS log viewer.

http://www.jeremytaylor.net/2012/07/14/sharepoint-uls-log-viewer-tool-comparison-and-verdict/