In the past few years, we have covered plenty of awesome theme developers here. The folks at AppThemes have some pretty unique themes (including ClassiPress which is one of our favorites). Their themes are fairly easy to customize. But you could always use these plugins to enhance their functionality:
ClassiPress Ads Importer plugin: lets you import ads and users to your ClassiPress site using a CSV file.
AppMaps: this plugin helps you get a better handle on maps in ClassiPress. It disables automate updating geo-location and gives admin more manual control.
AppAd Manager: adds Google AdSense ads between your posts in AppThemes premium themes.
ClassiPress Google Checkout Gateway: brings Google Checkout to the ClassiPress theme. Would come handy for premium listing sites.
Pronamic iDEAL: allows you to add the iDEAL payment method to your website. It supports WooCommerce, JigoShop, ClassiPress, and other platforms.
You are not limited just to the above plugins though. Standard WordPress plugins will work just fine with AppThemes themes. But the above scripts can save you time setting up your site.