Getting back links is central to website promotion - the more backlinks you have the more likely people are to find you, and as well as people, search engine spiders will index your site, and increase you pagerank. Amongst others, one source of backlinks is from peoples blogs - why not comment on what they have to say, while leaving a link back to your site? One problem could be finding the right blogs!

There is more to consider than that though, links count a lot more when the come from a site thats related to yours - so just spamming a load of unrelated blogs isn't likely to help you much. Get (comparatively) too many links from blogs and you might be tagged as in a bad neighbourhood, or be penalised in your site rankings. Another problem is that many blogs have the 'no follow' attribute set, which means your back links won't be followed by spiders anyway!

There is a tool;

Real Link Finder which can help you find some back links.

I will leave it up to you to decide whether this counts as black hat, or white hat SEO, and its up to you how much you use it! But, it can help you narrow down quality back links to your site - perhaps when used in moderation? A downside is that the email address you provide gets spammed by the program creator Neil Shearing!