GUI Programming for Newbies

Here, i'd like to give hints and pointers to programming a nice GUI for your programs. Though a GUI is not a must with linux, and even cumbersome for some applications, it's quite important for end-users and such.
Since you visit this page, I suspect you are new to GUI Programming, so i will introduce you to some widely used GUI API's and provide some links to tutorials and further Documentation.
On your first visit, take a look at the section "X11", which is a quick intro to
Eerm, as you see it sorta ends here: for the time being a linklist will follow:
Nils Juergens