At your budget, AdWords is really your best option. You should note that AdWords DOES allow you to do banner advertising and they also allow you to run Site Targeted campaigns, where you can specify sites in the Google AdSense network to run on.

I think it's cost effective to advertise in few tech forum which are populated enough like techguy.org/ tech-forums.net ect.

There are few options that are suitable for technology companies. I would be happy to help you with any of them:

- thought leadership - lead generation with white papers, case studies, web casts, podcasts.
- working with us on Pay Per Deal model is a very lucrative option for you. We engage our affiliates to sell for you on commission in a very unique way (both [process ad technology are designed for tech companies and B2B marketing). We will supply you with lead management system as well when we will be setting up your campaign.
- targeted email marketing to decision makers can be another option, a bit costly thou if you pay for lists and impressions. We also do it on Cost per deal terms.

I recommend creating whitepaper in slides format and share it on slideshare with the right keywords. Then, join a few Linkedin groups that you think the members may benefit from your technologies and then share a link to your slides and some information about how the technology helps these potential clients. You may also want to attach these slides to your website so you can track these visitors with your web analytics.