AppShopper has a great list of all the iPhone apps that have been recently discounted.
Technically, this isn't a Black Friday list. iPhone apps are discounted (and given price increases in some cases) every day. Still, there are definitely some deals to be had today, as MacWorld notes. Application development house Pangea has slashed prices on several apps including Nanosaur 2, Billy Frontier and Bugdom 2, all of which are normally $7.99, but today are only $0.99. The great game Enigmo, is also discounted today from $1.99 to $0.99.
The best part about Black Friday iPhone app shopping is that you get to avoid the insane crowds of people. Not to mention that you're likely buying these apps for yourself. Also, iPhone apps are better than socks.