bookmarks on books been read in different time and steel having value:

http://samizdat.mines.edu/howto/HowToBeAProgrammer.html?p=1#id2854043: How to be a programmer. good and short.

http://www.yendor.com/programming/unix/apue/apue.html - classical book by Stevens. Very good one.

http://www.advancedlinuxprogramming.com/ not such a good as AUP book by Stevens, but worth to see.

http://www.cs.fsu.edu/~xyuan/cop5570/ - another advanced source, .ppt with examples.

http://catb.org/~esr/writings/taoup/html/ Art of unix programming - very good for understanding architectural principles of Unixes.

http://www.khmere.com/freebsd_book/index.html

HOT:
http://www.tldp.org/HOWTO/Linux+FreeBSD.html