Microsoft has released the first non-beta version of the the Windows Defender product. Formerly known as Windows Antispyware, this product works with Windows XP and Windows 2003, and will be available in Vista versions as well.
There is also notice that Windows Defender (Beta 2) expires December 31. It would be a good idea to update your copy before then.
It is recommended that you uninstall the beta version before installing the new version. I first tried installing my new copy of Defender over the beta product, and I was forced to reboot to complete the installation. It probably would have been best to uninstall the old version first. Given that Defender ties into IE7 and Windows Live OneCare a reboot is probably necessary for most setups. Other anti-spyware products often require a reboot as well.
Defender is the old GIANT antispyware. Microsoft bought them out in 2004. It was one of the best in its day and it's still better than most of the free applications out there today.
I ran Spybot on a machine with Windows Defender. Spybot found hundreds of issues that defender apparently missed.
Spybot and the Lavasoft product....along with several others are notorious for tagging browser cookies as spyware. I'm not sure if that is a good measure of quality. Defender doesn't go after browser cookies, so that might not be an equal comparison.
It's good to have AdAware and SpyBot in your arsenal as well, but don't discount Defender.