I’ve previously talked about the distinguished BuySellAds banner marketplace. The network makes it much easier to sell ad space on your website, and has proven to be an excellent alternative to directly making deals with advertisers.
The Buy Sell Ads WordPress Plugin, once installed, allows you to insert an ad zone into your sidebar simply by dropping a widget in. For ads elsewhere, or if you don’t have a widgetized theme, you can use a template tag instead.
You can toggle some options like whether or not a placeholder ad should be displayed (recommended), and whether the ads should have nofollow attributes (also recommended). There’s also a field for editing the ad CSS.