FireFox and Thunderbird
Since I’ve started using the open source FireFox browser and Thunderbird email client rather than Internet Explorer and Outlook, Ad-Aware has found practically no spyware on my computers. With Outlook and IE, I was scanning for spyware every day and Ad-Aware usually found 5-15 new spywares. Today, I scanned both of my main computers for the first time in 5 days, and Ad-Aware found nothing.
I attribute this to Thunderbird and Firefox 1) defaulting to security on, rather than off as Microsoft does, 2) having better security options, and 3) not being targetted by viruses and spyware.
I’m also finding Thunderbird has a reasonably good spam filter plus a handy option where email from anyone in your address book is never considered to be spam.