Network Sniffer
http://ethereal.zing.org/

Exhaustive 'make' tutorial.
http://www.gnu.org/manual/make/html_chapter/make_toc.html

tcl tool
http://www.ede.com/free/tkdiff/

To detect memory leaks & run time error
http://www.parasoft.com/products/insure/papers/tech.htm
ftp://ftp.perens.com/pub/ElectricFence/ (also
http://lists.perens.com/mailman/listinfo/electric-fence)

http://cscope.sourceforge.net/
http://cbrowser.sourceforge.net/
 

1. Network Buffers and Memory Management - by Alan Cox
http://www2.linuxjournal.com/lj-issues/issue30/1312.html

2. Kernel API changes from 2.0 to 2.2  - by Richard Gooch
http://www.atnf.csiro.au/~rgooch/linux/docs/porting-to-2.2.html

3. Kernel API changes from 2.2 to 2.4 - by Richard Gooch
http://www.atnf.csiro.au/~rgooch/linux/docs/porting-to-2.4.html

4. Tour Of the Linux Kernel Source - by Vijo Cherian
http://www.geocities.com/vijoc/tolks/tolks.html

5. Linux 2.4 Kernel Internals - by Tigran Aivazian
http://www.moses.uklinux.net/patches/lki.html
 

The Unix Guru Universe : http://www.ugu.com/

Unix vs NT : http://www.unixvsnt.org/

Unix Programming : http://www.softlab.ntua.gr/unix

Unix Reference Desk  : http://www.geek-girl.com/unix.html

A few Linux pages :

http://www.linux.org
http://www.linuxresources.com
http://www.kernel.org
http://www.LinuxMall.com
http://www.gnu.org
http://www.slackware.com
http://www.slackware.org
http://lxr.linux.no
http://www.onlamp.com   [   For Linux + Apache + (MySQL | PostgresSQL )+ (PHP | Perl |  Python)     ]

In addition to this u can log on to http://www.internet.com and http://www.wdvl.com for the latest updates.