For the longest time the most commonly used ULS Viewer for SharePoint was located on the MSDN Archive Gallery. Today you can no longer find it there.
It appears that Microsoft has moved the ULS Viewer to the Official Microsoft Download Center.
I’ve also stored a copy of the application to my OneDrive account – just in case Microsoft decides to move it again. (ULSViewer.exe)
Want to learn more about the ULS Viewer? Check out Bill Baer’s post ULS Viewing Like a Boss.