Nate Silver has written an interesting data-based article on assessing the randomness of plane crashes—in other words, if you should avoid flying airlines that had crashes in the past.
an airline’s track record tells you something about its probability of future crashes — although not a lot, and only if looked at in the right way. In particular, you should look toward an airline’s rate of dangerous incidents of any kind rather than its number of fatalities or fatal accidents. These near-misses are more consistent from period to period — and could result in a deadly crash the next time around.
The only certainty? To minimize your risk, don't fly airlines from developing countries.