I can't say enough about ScribeFire. It's a Firefox add-on that gives you an in-window blogging client. Here are just a few reasons why it's awesome:
You're blogging from within Firefox, and you can move among webpages while keeping your blog post editing window open. This comes in really handy when looking for references, quoting things, finding pictures, etc. It also makes it really easy to fire off quick posts -- no need to open up a new window, log in, etc., etc.
When you copy something to your clipboard, it's automatically pasted to the "insert link" dialog. So, for example, you go to a webpage (while keeping your editor open, see #1 above) and copy the URL from the URL bar. Then you highlight your text and click the "add link" button. Bingo! The URL is already pasted there, and all you have to do is press OK. Sweet.
You can write to multiple blogs from the same place. Very nice. Also a bit dangerous, as you could conceivably post to the wrong blog very easily. Hasn't happened to me yet, but I do have a lingering uneasy feeling about it.
So, if you blog and you use Firefox, get Scribefire. Go get it now. I promise you'll thank me.
