It depends what your blog is about, where your target audience is located and what your budget is. Theres no point in just submitting a site to hundreds of free general directories these days.
Dir Submission have important role to get back links & Improve the ranking on target keywords & Page Rank.
You can get a free list of Directories from Directory Critic. Based on that you can submit your website/blog to those directories.
IF you are looking for directory submission then go for directory critic or vmoption it will really help..