(Needs to make a page more organized. My apology for a messy arrangement.)
Esri Udemy Online Course: https://esri.udemy.com/
If someone is working on or interested in Global Information System and Remote Sensing, ESRI website, tutorials, online library and many resources will definitely make learning easier. Also, Hexagon Spatial [http://www.hexagongeospatial.com/] is another wonderful site to learn about remote sensing and GIS. This link, http://fas.org/irp/imint/docs/rst/Front/tofc.html, will also be useful to learn about Remote Sensing and Image Processing.
Geotech Centre: http://www.geotechcenter.org/
Online Sources to Download Landsat Database:
USGS Glovis: (USGS Glovis is an online database to download different images and other data related to remote sensing and GIS as well as related fields.
These links provide quick guide and information about Landsat project, Remote Sensing GIS and related issues:
Landsat LooK Viewer: Prototype tool that was developed to allow rapid online viewing and access to the USGS Landsat image archives.
Landsat Science: http://landsat.gsfc.nasa.gov/
Path Row Finder: http://landsat.usgs.gov/tools_latlong.php
Digital Globe for high-resolution Images.
GIS/RS Stakeholders in Nepal and Data Portals