Any tips on ad retargeting?

We're about to launch a new product, and we're expecting (hoping for) a bunch of traffic from HN and other tech sites.

In the future, I'd like to be able to buy ads to target the initial wave of visitors. We're a SaaS product for developers, and so these visitors will be our perfect target market.

Does anyone have good experience with ad-retargeting services? Any tips for how we can do this on the cheap?

thanks