Also, just a heads up: there's no "official" Bitcoin logo.
I think it is fair to say that the most recognizable and probably the most used Bitcoin logo is designed by member bitboy, back in 2010. This is one of the first logos that were created for Bitcoin by a community member. It is a simple design, and it has proven to be timeless.
Hi guys, just drop by to say hi and to share with you some of the graphics I have done, feel free to download. All files are in PNG format, and almost all of them with transparent background. Hope you will find them useful.
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I do not know why the images are no longer available in the original post, but anyone can find them in the archived version: https://web.archive.org/web/20130525203057/https://bitcointalk.org/index.php?topic=1631.0;all
Best of all, according to the author: "Everyone can make use of the graphics freely even for commercial purposes with this license and not bound by any restriction."