How does your site do for organic search results ? So not just the paid ad's down the right hand side or at the top but the regular results that are returned when people search for the keywords that your paying for, if your not on the first page then you should spend some time or money getting yourself there as thats worth a lot of traffic and potential leads.
When we first started up we used google adwords for a few months whilst we worked on our SEO but once we got to the first page and at the very top for some search terms we knocked our Adwords spend right back to virtually nothing, no point spending money every month for something that can be acheieved for free.
Blogging is the other thing thats brought us traffic and leads, people feel connected and keep coming back and their friends, work colleagues etc see what they are looking at and word spreads that way.
Less traditional means like facebook is the latest one were working on for generating leads, having friends tell their other friends about you is a more powerful than advertising imo.