Ask HN: Good books on similarities, searching, recommendations etc?

Being a self-taught engineer/programmer I ommitted many useful topics I should have learnt some time ago.

A few weeks ago I started reading "Programming Collective Intelligence" by Toby Segaran [1] and I think it was a very good start to learn about the subjects mentioned in the title.

It puts nicely theory into practice and everything is quite easy to understand so it's a great introduction, but I'd like to learn more :)

Can you suggest any other good and intelligible books on topics such as recommendations, filtering, similarities, clustering etc.?

1. http://www.amazon.com/Programming-Collective-Intelligence-Building-Applications/dp/0596529325