Could anyone recommend a more or less 'respectable' free banner exchange site?

I use Google Adsense on my site, but I like to rotate in banners from banner exchange sites every once in a while. The reason for this is that I like to get advertising for my own banners every once in a while, but don't wish to pay Google for such a service

The only problem is that so many of the ads that come up on banner exchanges are trashy. Are there any places anyone would recommend?