Know-How Exchange : SEO/SEM

We're investing in our SEO practice, and have been able to move up significantly in most of our keywords (e.g. from unlisted to page 2) mainly through better content and site design, but now that we're knocking on the "first page" door, we're finding that we're hitting a plateau.

Most of our keywords have fairly small LMS (under 2,000), with varying levels of competition.

One area we've really not focused on heavily has been link building because A) it's so tedious and time consuming to do internally (we just don't have the people resources to dedicate to doing it effectively) and B) there seem to be a ton of black-hat, less-than-professional link building consulting services out there. I see examples every day as I'm cleaning out our blog's spam folder.

Does anyone here have experience in hiring/working with reputable and effective SEO companies that focus primarily on above-board link building? Would you be able to provide some recommendations? Would you be willing to share some information on how much it cost you?