I'm thinking that all the default fonts that come with say, Windows XP, don't need any mention, and most free fonts from the internet are the same way - but there are exceptions, and the creater should state in a file included with the font if it is a free use font or not. Probably doesn't help you much - you'll need to check with the creators.
Edited to add: Fonts that are unique to a brand usually CAN'T legally be used for profit, but it never hurts to email the company and say hey, can I use your font, I'm making "this".
