Your safest bet is to use only fonts that are stated to be free for commercial use and/or free for redistribution.
When I realised I had a lot of different fonts and had no idea which I could use in my commercial kits, I did a "font cleaning". I Googled every font I liked to use, and hunted down the TOU that way. Some I re-downloaded because I had lost the original file with the TOU. Surprisingly many were not free for commercial usage, and what I did was simply delete that font from my hard-drive (because I can't trust my cardboard head
).
I remember seeing a post here with links to sites with free, commercial fonts. Maybe do a search?
