If Tk doesn't look old and crufty anymore, you wouldn't know it from the official website: there are no screenshots to be found. I spent five minutes trying to see what a modern Tk GUI looks like then gave up.
http://www.tcl.tk/man/tcl/tutorial/tcltutorial.html
Most of the actual material is Clif Flynt's though. It's not perfect, but at least it's a starting point that's widely visible to people getting going with the language.
And, of course, it's Tcl, whereas you're asking about Tk. Definitely something that would have been useful.