While The Warden may run in the background and snoop what you have running, this is hardly spyware.
Spyware is malicious. It sends personal data to 3rd parties to use for monitary gain. The Warden sends program data (even if it is regarding all running programs) to Blizzard to determine hacking methods used.
This actually strikes me as a bit of a paradox. People hate cheaters. Lord knows that I do, but many people are clearly not willing to accept the steps that Blizzard has taken to prevent cheating in it's online world. I would imagine that The Warden is very effective at what it does, even if it's methods are somewhat questionable (although perfectly legal. Do people even read the EULAs anymore?).
If you don't want The Warden snooping what you have running, then turn off whatever you don't want it looking at. If you don't want The Warden running on your system, then uninstall World of Warcraft, cancel your account, and contact Blizzard for a refund, stating that you do not agree to the EULA (the EULA that you should've read when you installed the game, and after every patch revision).