self destructing mailing service....
here is the link for some self destructive mailing service...these mails can be read once only and will be deleted chosen by sender...
http://thinkabdul.com/2007/07/25/ten-free-services-to-send-self-destructing-emails-which-expiredisappear-automatically-after-specified-time-interval/

electronic e-books
here is the schaum's circuit analysis e-book...
http://www.esnips.com/doc/3215623e-f247-480b-9ce9-9e80ebaa351b/Schaums-Electronic-Devices-and-Circuits
u can scrap me for more e-books....
http://www.orkut.com/Home.aspx?xid=7935095215260433472

puzzle site
this one is a very cool puzzle site...mit kids made that...
rec-puzzles.org/