Blogging is a very ego-driven endeavor. There are hundreds of thousands or millions of blogs out there and most aren't read by any large number of people, and yet people still write their blog because they like to think they are important, they like to think they matter, and they like to think people want to read what they have to say.
For some sites or specific industries, and for many ecommerce sites, you can exploit this by reaching out to bloggers for promotional purposes. Old-school brick & mortar promotion is sending out press releases, buying newspaper advertisements or TV ads, maybe hiring a PR firm. Web 2.0 promotion is getting bloggers to talk about your product or site to build buzz and generate traffic and links. The Web 2.0 method also happens to be cheap.
If you have a website or product you are selling that a blogger could possibly review, send them an email asking them to review it. If you're selling a product it is easy to sweeten the deal as you can simply give them a free copy in exchange for the review. Bloggers like feeling that they're important enough to be picked by a company to review something and get free merchandise, but they don't like feeling bought, so stress that you're not seeking a positive review, but an honest review.
The review the blogger writes will undoubtedly include a link back to your site, it may spawn blog posts at other sites, and will send direct traffic in addition to helping with your search engine rankings.
You'll want to find the most popular independent blogs for this sort of thing, the easiest way is to search on Google for your keywords and "blog" and see which blogs rank at the top. If you cannot find a contact email leave a comment on a recent post and ask them to email you.
Assuming your product doesn't really suck you'll probably get a good review anyways. People by nature are good and if you're nice and respectful to the blogger and give them a free product they'll feel guilty if they write anything too bad. Even if they do end up not liking the product they will likely say that it is just their opinion and they could see how someone else would like it, and in the end there is no such thing as bad publicity.
An easy way to gain incoming links, though those of questionable value, is to participate at related forums and blogs. Almost all blogs and most forums allow posters or commenters to leave a website link or have signature links and you can gain direct traffic through these links in addition to gaining link popularity.
The key though is to participate in a real fashion. There is software or services out there that will automatically post rubbish at forums and blogs to get you links, this is spam. There are also people out there that'll do such posting manually but only achieve a level of quality a sliver above the posting robots, and that's still spam. You need to participate, not just post. You cannot simply say, "Yes, I agree" and hope to not be perceived as spam.
The best advice I can give in this regard is to try not to post anything you wouldn't post if you weren't trying to get incoming links. The idea of gaining links from forum signatures and blog comments should be more about getting some links & traffic for an activity you'd do anyways, rather than an activity you're only doing for the links. Blog & forum owners tend to be savvy to this sort of behavior and may end up banning you for it if you're not being genuine.
Also, remember, the more helpful you are the more people will respect you and the greater exposure your links will get.