I can recommend all of the following, with the Dudeney book and those published by OUP being particularly good for one-off lesson plans based on a particular website/page.
- The Internet and the Language Classroom, Dudeney, G. (Cambridge, 2000)
- Dave Sperling's Internet Guide, Sperling, D. (Prentice Hall, 1998)
- How to Use the Internet in ELT, Teeler, D. and Gray, P. (Longman, 2000)
- Internet and ELT: the impact of the Internet on ELT, Eastment, D. (Summertown Publishing, 1999)
- Internet English Gitsaki, C. and Taylor, R. (OUP, 2000)
- The Internet, Windeatt, S., Hardisty, D. and Eastment, D., (OUP, 2000)
- The Internet and Young Learners, Lewis, G. (OUP 2004)
- Teaching English with Information Technology, Gordon-Smith, D. and Baber, E. (Modern English Publishing, 2005)
Note that most of the above — all published fairly recently — make no mention of blogs, one of the big phenomena, the big success stories, of the Internet. Some don't even mention Google! What is published about the Internet quickly becomes dated (note particularly how the links the books give will quickly break).
Some publishers have companion websites for their "resource books" (also course books) — partly to combat this problem. The three OUP books above all do (registration required):