What are the best books you suggest me about:
HCI for web applications / websites
Jakob Neilson's Don't make me think is a good primer; after that it depends on what you want to achieve.
For instance Toby Segaran's Programming Collective Intelligence and Leonard Richardson's RESTful Web Services have helped deliver HCI benefits and "the feel good factor" far more on projects than any usability book I've read so far (be careful not to throw the baby out with the bathwater, they are still useful).
If you've not seen anything on eye-tracking results, its certainly worth a look (many books offer you a free chapter on-line and some reports are available for free).
Afterwards it is worth having:
There's a similar question on the UI SE site. Not about the web specifically, but probably pretty relevant. Some good responses there.