Rating sites
Submit your site to some of the websites that rate and rank products...you get a referral and pay them, but it's likely cheap, concentrated, relevant traffic.

Industry Portals
More concentrated traffic...makes sense and it's inexpensive compared to other methods.

Conference and Planned Meeting events
Conferences and exhibits are planned and presented in order to generate cash and offer industry exposure.  We suggest that our clients use them for their connections and to get relatively inexpensive eyeballs.  Sometimes, these short-lived events and concentrated numbers are great traffic sources.