Fixed spots:
http://www.ero-advertising.com/buying-spaces.php
Or use the THUMBads
www.ero-advertising.com offers where you set your own pic (and texts above and beneath it if you want). You can block any source/url and use filters such as pagerank, GEOip, language, country, etc.:
http://www.ero-advertising.com/en/ad...ers/thumb.html