Some Useful Goldsource Modding Resources
Goldsource modding tutorials are uncommon and are hard to find today. Many sites can only be viewed in the wayback archives. It is very hard to locate these resources (I couldn't find many of them on google) so I will post them here for everyone's convienience.
Russian Goldsource Modding Forum:
I can't read Russian, so I use a translator, but be aware that this messes up some code, so disable it when copying or reading code snippets.
Half-Life Programming Planet
Wayback's Archive of HLPP
This was available until mid 2013. Not sure why it's not anymore.
Old wavelength Tutorials:
Then theres of course Gamebanana, but there aren't many HL tutorials there.