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?