Hi Mark,
- Contact blogs in your niche and offer them products to review and keep (with a couple of links back to your site) or giveaway on their blog (again, we a couple of links back to your site). This works really well when a review and giveaway of the same product are done at the same time
- Sign up for forums in your niche and actively start posting valuable content. Don't spam, be transparent about who you are, but offer genuine, useful content and discussion.
- Analyse OSE every reindex and copy your competitor's best links! Be it in niche directories, blogs, high authority informational sites etc etc
- Get social - sign up for FB, Twitter, Pinterest, G+ etc and become active - share, like, follow, comment etc (regularly!)
Hope this helps,
Brad