Just to complement the previous post, another software you can use to create blogs in the Apple platform is iBlog Product Page, from Lifli Software.
The difference from this program to MarsEdit, however, is that it does not interface with blogger systems, such as blogger and moveable type. Instead, it can be used to manage itself the blog.
In this sense, iBlog is similar to iWeb, recently released by Apple, since iWeb can generate its own blogs that are upload to the .iMac account.
MarsEdit: editing your blog on an Apple Mac
Apple iLife and iWork have new versions