There appears to be a blog on just about any topic you can imagine, including quite a few on genealogy.
Facebook maintains a listing of the Top 50 blogs in genealogy...
If you are not sure what a blog is or how to create one, BlogBasics is the site for you. They offer a Blogging for Beginners tutorial that discusses the fundamentals of blogging as welll as outlining the choices you need to make in deciding how to implement your own blog.
Lisa Louise Cooke has created a four part video series titled "How to Blog Your Family History". She offers suggestions on possible genealogy related topics as well as an in-depth overview of how to create a blog using Blogger, a free service offered by Google, which is a really good choice if you want to create your own blog:
If you are interested in creating a blog on your own web hosting service, WordPress is probably the best way to go. The software is free and widely used (it is what the Dallas Genealogical Society is using). See their web site for more information.