Software Testing Hotlist
The best source of information on Expect is the book Exploring Expect by Don Libes published by O'Reilly. It contains an excellent tutorial on Expect and it's underlying language Tcl (Tickle). Expect itself is freely available. For more information on how to obtain it, see the Expect Home Page. Once you start using it, you may want to review the Expect FAQ.
DejaGnu is a framework built on top of Expect to support testing. It is also freely available. Its documentation is online.
Other information on Expect
Other information on Tcl
Books on Tcl