I would leverage guest blogging, either on and spend your time link baiting/viral marketing/content marketing, whatever you want to call it.
There are tons of options for the link baiting/viral marketing content:
- A contest
- A tout or rankings badge (target "featured companies" or rank blogs in your industry, especially if your directories have cred in the industry)
- An infographic
- A comprehensive guide or resource list
- A list ranking the top companies for a specific product or service in a specific industry
- the possibilities are endless
The benefits you will find here are that you can build content for your guest blogging around the link bait as well as issue a press release about the link bait. I would suggest avoiding just picking a popular consumer electronic as a prize and actually come up with something relevant and creative for your industries. This way, you don't receive links through your social media networks and blogs that say things like "go win an iPad" and instead say things like (example) "win a remodel of your ugly bathroom."
The guest posting and PR distribution will build a volume of quality links to your homepage or other targeted ranking page, plus the links you get to your piece of content will increase the overall authority of your domain.
Plus, with all of the links being cohesive, the engines will be able to easily determine relevance for your website.