Haven't learned about Ninite before - thanks for that!
Paint.net is an awesome light little program as a replacement for MS Paint, so long as you don't mind installing .Net 2.0
One of my first downloads for every new install is
ProcessExplorer as a replacement for Windows Task Manager.
For PDFs I avoid Adobe Acrobat - bloated and insecure methinks. Instead I like
PDF X-Change Viewer, which adds some editing features and browser plugins.