Oddly enough, I was just reading this about two weeks ago:

"Another way to look at things is to order the batting slots by the leveraged value of the out. In plain English (sort of), we want to know how costly making an out is by each lineup position, based on the base-out situations they most often find themselves in, and then weighted by how often each lineup spot comes to the plate. Here's how the lineup spots rank in the importance of avoiding outs:

#1, #4, #2, #5, #3, #6, #7, #8, #9

So, you want your best three hitters to hit in the #1, #4, and #2 spots. Distribute them so OBP is higher in the order and SLG is lower. Then place your fourth and fifth best hitters, with the #5 spot usually seeing the better hitter, unless he's a high-homerun guy. Then place your four remaining hitters in decreasing order of overall hitting ability, with bases stealers ahead of singles hitters. Finally, stop talking like the lineup is a make-or-break decision."

Optimizing Your Lineup