What is the YouTube logo font?
The font used for YouTube's iconic logo is Linotype’s "Helvetica Ultra Compressed".
Some versions of the YouTube logo also include the catchphrase "Broadcast Yourself", which is in the font "Helvetica Neue 55 Roman", also by Linotype.
To view a complete list of the Helvetica font family, you can view the Wikipedia article here.
To purchase Helvetica Ultra Compressed, you can find it at FontSpy.com.