The best way would be to use google advanced search and type into the box that says exact word or phrase whatever your niche is. Then click on the More option and select blogs. By doing this you will find all blogs related to your niche.
Use Google Blogsearch option. Type the keywords related to your niche into the search box and go through the list. You will be able to find niche blogs that are wholly or partly related to your niche.
"add your comment" + "keyword" Example - http://www.google.com.au/search?hl=...+comment"+++"cars"&btnG=Search&meta=&aq=f&oq=
Technorati.com - it's a blog directory, you can find blogs by category, by tags - the top blogs in a category, by searching for keywords etc etc etc You can also use Google alerts for this - set up an alert for your keywords and specify that you only want blog alerts. You'll get reports when your keyword is used in a blog post - doesn't necessarily mean that the blog is in your niche, but you'll get notifications when your topic is being written about in a blog post.
Seldom do I find such an excellent, well written, easy to follow answer on DP. I remember trying to find relevant blogs for a project using simple Google. It was an arduous process. Thanks for asking the question but even more for getting this answer...
or you may use blogcatalog download free version of some blog finders out there such as fastblogfinder etc.
I just started using Google alert too, plus just go to Google blog search. Commenting can take ages. I need to find gadget blogs cuz I own a ebook reader blog.
There are quite a lot of blog search engines out there that you can use. One of them is blogsearch.google.com. Just type in your keywords and viola!