xCake Ads Lite allows you to add banners to your sidebar via a widget. Still in beta-testing mode (expect daily updates)
Currently only Portuguese (pt_BR) and English. Default is English.
Head to http://wordpress.org/tags/xcake-ads-lite?forum_id=10#postform and leave a question. If you have found a bug, please report it to canha at xcakeblogs.com.br with as much info as you can (what did you try to do, what error appeared, etc).