I used to use Windows Live Writer in the old days but now I'm a trendy Mac user I need something suitable. Seems like there are a number of paid options that people rate quite highly but I'm too cheap to pay for software.
I just tried Quamana and it looked promising. Unfortunately it kept throwing errors, didn't download tags from Blogger and then failed to actually publish the post!
I'm now trying Flock which is a full featured browser built on the same stuff as Firefox, that happens to have a blog editor built in. I don't think it's as clean as Live Writer, but appears to have enough functionality for my basic use.