This is a good question because I too have found it curious that some weblogs at Blogger (a wholly-owned business of Google) have the little navigational toolbar on the top while others don't, and wondered how that was accomplished. The toolbar's called the Blogger Bar, by the way.

First off, though, here's what we're talking about:

To eliminate it, simply add the following CSS to your template:

However, please be aware that this is probably a violation of the Blogger / Blogspot Terms of Service, which perhaps obliquely state:

"Pyra runs advertisements and promotions on BlogSpot Sites. By creating your BlogSpot Site, you agree that Pyra has the right to run such advertisements and promotions. You also agree that you will not attempt to block or otherwise interfere with advertisements displayed on your BlogSpot site via JavaScript or any other means. Doing so is grounds for immediate termination of service. The manner, mode and extent of advertising by Pyra on your BlogSpot Site is subject to change."

The ToS is mildly amusing reading, by the way. My favorite bit: "Now, this next part seems really damn obvious, but everyone else has it in their TOS's so someone's probably gotten sued for not having it. So: In order to use the Service, you must obtain access to the World Wide Web."

There is some debate on this issue of blocking the Blogger Bar, however, as detailed in the Customizing Templates discussion group for Blogger Help.

Make your own decision on this, and good luck to you!