Mailing lists and Newsgroups are the ideal spots to target your niche audience. Search these mailing list directories to subscribe to mailing lists that reach people you want to reach. Think about who visits your site, then place the graphics and links strategically so that when your audience intercepts them, they will be most likely to click on them. Try different links and banners and see what works best for your site. Test different links and banners on different pages and measure the results.
Text links generate good click-thru responses as well.
If you aren't already using them, you may want to give them a try.