The consensus on the web is that Ecto is one of the best blog editors for the Mac platform. With Ecto I can interface with Typecast, manage my blog entries offline, use a real-time spell checkers, insert tags, attach images, etc.
While installing the application was the typical straight forward drag and drop routine, the configuration process took a little longer. Ecto was not able to automatically configure my Typepad account. I had to resort to Ecto support forum to find the correct settings - a process that took 24h altogether.
Note: the correct access point for Typepad is http://www.typepad.com/t/api
Ecto's license is $17.95, but you can download a trial version that will work for 21 days before you need to register it.
There is also a Windows version of Ecto for those interested, but I have yet to try it.