Our company is also looking at a way to stop Spyware, Malware, and the like.
Take a look at Greenborder.
It creates a locked down virtual machine for "untrusted" content to run in (IE and external E-mail). Unlike most solutions this lets everything run - both good and bad - but once you click "close" everything it was running is gone. No registry changes, no keystroke logging, nothing.
Our company looked at the product and we really liked what we say (it's not easy to impress an entire IT dept with a product). Although our management balked at the price (the one bad thing about the product) I think this is an innovative and secure way to prevent all this garbage from harming your network.
For security and it's ability to stop harmful material I give it a 9.5/10.
For price I give it a 3/10.
I know it wasn't on your list - but if you can afford it, I'd recommend it.
Zaf