Someone will say «Another client for blog posting» and it will be wrong. Post2Blog is one of the most convenient programs of this kind. Its main advantages:
Post2Blog used to be distributed as a shareware program, and now the developers have abandoned the idea of making money on it :) Download and work for free.
When I was working on Windows, I really liked this client. The only drawback for me was how the insertion of pictures was arranged — it was impossible to specify the exact dimensions for the sketch of the picture. The rest of the program is excellent.
Platform: Windows only.
Price: Free