OWaechter - OGame RSS Reader
Unlike OGam3r RSS Reader, this one is free, but only works on ogame.de.
The program will conveniently nest in your system tray and notify you of any scans, transports, attacks etc.
There's also a number of features planned like battle report archives, startup options, remote warnings and more.
I hope it will work soon on ogame.org and other localized versions. You can check OWaechter website for more info and download. There's also a forum available if you have any questions.