There are many sources of materials to support the teacher and the student. The most obvious are textbooks – on paper or on-line – and web sites. As long ago as 2009 I interviewed two graduates who obtained first class degrees from a major UK university: They asserted that they did not open a single paper text book during the four years of their programme. They had used many resources, but paper-based text books were not among them.
One source of resources is becoming available through the work of several projects on Open Educational Resources (OER). For several years MIT has offered its Open Courseware [http://ocw.mit.edu/] and the Open University in the UK has OpenLearn [http://openlearn.open.ac.uk/: Look under Technology as there is no separate Engineering section]. Both these institutions are now offering MOOCs which offer many of the advantages of open resources. The OER projects have tried to ensure that there is a single portal for each discipline which leads to resources of all types which are openly and freely available under Creative Commons licenses. This means that you can use, distribute and even modify other people’s educational resources as long as you do not sell them on. There is a single repository for all these in the UK, called Jorum Open [http://www.jorum.ac.uk/] as well as subject-specific gateways which might be simpler to use [e.g. http://www.heacademy.ac.uk/disciplines/engineering-materials and CORE-Materials core.materials.ac.uk]. Resources available from these sites include photographs, videos, lecture notes, questions, animations, simulations and even in some cases whole books. This book is itself available as an OER.
Recent work at Liverpool by Andy Green and his colleagues at Liverpool has led to the development of a visual search engine, Kritikos, which enables the lecturer or student to find image-based material in a specific domain such as engineering. The resources, once discovered and used, can be rated for relevance and quality. You can explore this facility at kritikos.liv.ac.uk.
There are plenty of other resources, many of which cannot be accessed through a single site or URL. Appendix 1 includes a fuller list of resource sites.