Authors: Brent Welch, Jeff Hobbs, Ken Jones
Publication date: 2003
This book is now available.
This book is up-to-date with Tcl/Tk 8.4.
The book's home page is http://www.beedub.com/book/
There are about 20 sample chapters available at [L1 ] taken from the 4 editions. They cover topics from the basic Tcl and Tk introductions, through more advanced topics like Regular Expressions, Eval, Socket programming, Thread programming, TclHttpd, and Starkits.
A few general remarks on the book appear in the review [L2 ] by Cameron Laird, as well as this [L3 ] follow-up review.
Among its other virtues, the fourth edition explicitly explains use of Tk by such other languages as Python, Ruby, Perl, and so on.
Special offer, see the UK's Register website - http://www.theregister.co.uk/2004/04/27/tcl_tk_programmers_bible/
2008-10-22 : I wonder if this one is going to be update for 8.5 and Tile?
peterc 2009-02-16: This is an excellent book for a programmer of other languages who wants to get stuck into Tcl/Tk. It assumes some familiarity with basic programming concepts though (for me, a good thing; less of the book is wasted explaining the basics of what a variable is, etc) and this may make it a little less approachable for complete novices (well, those who have no Internet access or ability to use a search engine [L4 ] to find more information, anyway).
Anyhow, suffice to say, if your budget only stretches to one book, I'd recommend this one. Yep, it's currently missing discussion of Tile, but, if you learn how to use Tk from this book, you'll be able to pick up and use Tile immediately.