Once you've identified potential partners that are serving a similar target niche you can do article swaps with them to help spread your message. Blog swaps or newsletter article swaps allow both of you to gain exposure that you otherwise would not have had. Often industry-specific blogs are open to guest articles as well.
Even if the other list owner or blog owner isn't interested in sending you an article in exchange, you'll find that many are open to posting your article simply to provide their readers with quality content. You won't know until you ask!
Don't just look for blogs in your niche. Try to find markets that serve on the edges of your market, but that serve a similar demographic. For example, I've found that real estate investors tend to respond very positively to my Internet marketing advice articles—even when I have no mention of real estate in the article.
When you guest post, ask permission to insert limited links into your article. Don't overdo it. No one wants to load up their blog or website with links sending readers running away.
Reassure your blog host that you will be promoting the article to your reader base once it is posted on their site. This is a great way to return the favor for their kindness.