A list of databases and indexes covering Chemistry and related areas (Materials Science, Physics)
Note: CAS Scifinder-n requires registration. Please email firstname.lastname@example.org for the URL.
There are lots of classroom materials of chemistry lectures, problem sets and exams on the web:
The video below is from one of the many collections from the Royal Institution's RI Channel in the UK.
Khan Academy has many introductory chemistry lecture videos. Note that problem set solutions may be locked.
CrashCourse has videos on Chemistry course topics.
MIT OpenCourseWare has lectures, problem sets and exams online.
UCI Open has lectures, problems and solutions in individual lectures.
The Organic Chemistry Tutor covers many topics in Chemistry as well as Math and Physics.
Periodic Table of Videos covers many chemical topics.