Here you will find the GTK+ home page with lots of information about the GTK+ toolkit and links to several other related projects. If you need help on using GTK+ or just want to keep track of the latest GTK+ developments there are mailing lists you can subscibe to.
The Standard C++ Library
If you need help with the Standard C++ Library you will find its documentation online here.
Want some tips from the master. You will find Bjarne Stroustrup's web page here
The DevX C++ Zone
If you want to fine tune your C++ programming skills this site should be helpful. It has an archive of useful C++ tips, and is regularly updated.
Trying to build a great web site. HTML Goodies has lots of practical examples that show you how to add some great features to you web pages, like changing images on mouse over or displaying transparent images.
Looking for a good open source IDE for GTK/GNOME? Check out Anjuta.