There are several free and paid American-based products. I tend to recommend the free Spyware Blaster for home users and Webroot's SpySweeper for businesses.

To be clear, the two leading free anti-adware products SpyBot Search & Destroy and Ad-Aware are not American-based. However, unlike anti-virus software, you can run multiple anti-adware products at the same time and benefit from their combined protection. For home users, I like to make sure they have enough RAM and install both the American-based Spyware Blaster and the Swedish-based SpyBot Search & Destroy. That's a powerful combination. For our business clients I tend to stir them toward Webroot's Spysweeper.