If you :
* would like to have a further introduction into TRIZ, and you would not like to buy a TRIZ book
* would like to have a complete introduction to TRIZ, and you have already bought TRIZ books
* even are a TRIZ practitioner
you may be interested by the website of the TETRIS project.
In particular, the TETRIS project website provides (after due registration) the possibility to download a very complete TRIZ course. Five additional tough problems are proposed with usual mistakes and control solutions.
I forgot the following information : the access to the documents is for free. Very appreciable initiative !