Google likes to offer bounties. There's one for AdSense and AdWords, Google's ad features, and $1 for every new Firefox browser with embedded Google Toolbar user.
Google now pays $2 for every one Google Pack referral and $1 for every Picasa. Referrals are accomplished through a Web "referral button."
It's $20 for each AdWords referral that spends $100 on the feature, and $100 for every AdSense referral that spends $100 on AdSense.