Advertising fulfills two crucial roles in internet political advocacy.

1. It draws attention to important causes and issues, and provides a means for people to become involved... whether that means donating money, signing petitons... or participating in letter writing campaigns directed at elected officials.
2. It generates revenues to cover the expenses involved in hosting a popular website. Websites like DailyKos and MyDD would not be possible without the income provided by advertising.

Blueshifting designs advertising banners that perform - grabbing the attention of site visitors and attracting those click-throughs which are crucial to the success of your advertising campaign.