When discussing the historical reliablity of the Bible, the first and most obvious issue revolves around the supernatural. Unfortunately, it can also be the most difficult issue to resolve; most of these supernatural events were small scale and would leave no traces behind in any extra-biblical sources. The Biblical literalist is armed with an airtight defense: "God did it". The strangest events - such as Joshua praying for the sun to stop - can be explained and defended from this position. God is God. He can stop the sun. Umm... Earth. I'm sure the perfectly inspired and totally inerrant author of Joshua meant to say "Joshua stopped the Earth" when he wrote Joshua stopped the sun. It's odd how human perspective could over ride the physical truth in a 100% divinely inspired document. But nevermind that.
There are, however, at least two (and possibly three) stories that completely stretch the bounds of credulity.
The most fun of these stories is Samson killing 1000 men with the jawbone of a donkey. Here's the NIV version.
So. Picture the situation. A supernaturally strong man. He was supposedly strong enough to knock down two pillars, destroying a large temple and killing himself the the process - so clearly he wasn't invulnerable.
There are two possible scenarios, one more belivable than the other. The first is a Neo/multiple Agent Smiths battle. In order for Samson to kill 1000 men without being injured, he would have to move like Keanu Reeves on meth. Didn't any Philistines bring along a bow? Or a slingshot? I figure after watching one guy kill 100 of my buddies, I'd start to think it was time to run away. How could one man lay hands on 1000 men, even if they couldn't fight him or hurt him? And how did the jawbone survive cracking 1000 skulls?
The second scenario relies on a dodgy interpretation of the text. It's possible that Samson killed these men over a long period - not in one single battle. This is a bit odd, however - notice that Samson is extremely thirsty afterwards, and asks for a miraculous source of water. This indicates the killings took place between two periods of rest. Also, Samson refers to it as a singular victory, not a series of them.
Maybe I'm not applying enough imagination to the story. Maybe Peter Jackson could come up with a plausible scenario?
The second story is even better. As far as I can see, it forever nails shut the coffin of literal Biblical relibility. This neat little story is Noah's Ark.
Samson's killing spree requires a cartoonish series of miracles; Noah's Ark requires a seemingly infinite number of extraordinary events that should leave one asking why God didn't use a more efficient method.
Why would God induce a catastrophic global flood, then remove all evidence of said flood, then alter the geological column to make it look like a flood was in fact impossible?
How did North American or African species get to Noah? Many of these species require specific enviroments and food. Certainly sloths in South America and koalas in Austrailia woudln't have survived the trip?
I've been told that the continents were not separated before the flood - that the flood itself began the breaking of the continents. Well, the Atlantic ocean is 1700 miles wide at its shortest point. Answers In Genesis.com places the flood at 2304 BC, which means the continents have had 4285 years to travel 1700 miles. The continents, apparently, could shatter any NASCAR record and still manage to stay intact.
Dinosaurs had to be onboard, too. And not dinosaur eggs - remember, Noah had to take male and female. He needed hatched specimens. Does anybody want to speculate on how Noah and sons would care for a 12 month old T-Rex?
Disease would be another problem. How many diseases can survive in a population of 8 for a full year? Would the measles have survived? I guess it's a good thing none of Noah's sons had chicken pox as children.
The number of miracles needed to make the story work is astounding. I advise everyone to look at this page, from Talk Origins. It's a huge archive of the seeminly endless problems with Noah's Ark and a global flood. The story is, in terms of a literal historical account, childishly absurd.
The third story is the Genesis creation itself, but I'm not going to get into that right now.