Google now allows to change between Arial, Times, and Verdana font faces of the text in AdSense ad units on pages in Latin-character languages.

• To change font face of all your ad units: Visit the 'Ad Display Preference' under account settings to select a new account-wide font face.
• For existing ad units: Visit “Manage Ads” and updating your font choices for specific ad units. The changes will be maintained even if you change your account-wide settings later.
• For creating new ad units, you’ll be prompted to select between the default 'Standard AdSense font family', your new account-wide font face (if you've selected one), or another font face.