http://www.bannerswap.com/ supports 160x600 ad formats and 500x30 on a 2 to 1 exchange rate among other formats.

http://www.skyscraperads.com/ a 120x600 skyscrapper ad exchange with a 2 to 1 exchange ratio.

http://www.trafficflame.com/ a 120x600 skyscrapper exchange site with a 5 to 4 exchange rate that can be reduced to 2 to 1 for poor performance. Ad creatives are served from the publisher's servers this could result in a slow loading ad from a member site slowing down your page load speed. It is suggested to test them before fully using them. They also support regular banners.

http://www.flashbanners.org/ supports 120x600 skyscrapper ads on a variable exchange rate starting at 4 to3 ratio with some free credits on sign up.

http://www.e-bannerx.com Provies support for 120x600 ads on a 3 to 2 ratio with advanced targeting.. This exchange supports the selling of exchange credits between its members.