Q:

What's the best way to store lettuce in the refrigerator?

What is the best way to store lettuce in the fridge? 

Should I store it in an airtight container, or an open bag?
Should I wash and cut it first?
Should it be stored wet, or patted dry?

A:

It depends on what type of lettuce it is -- part of the issue is that if the lettuce is touching plastic, it will rot quicker, so I wrap it in paper towels, then bag it (but not sealed), and keep it in my crisper.
For whole heads of lettuce (iceburg, butter, red leaf, etc), I just wrap the whole thing in dry paper towels, then shove it back into the bag from the grocery store or farmer's market.  I then pull off leaves as I need it, and re-wrap it.  It stores for well over a week this way.
For mescalin mixes, arugula, or other individual leaves, I'll wash them, dry them, then unroll enough paper towels to spread the leaves on, then roll up the whole thing, and bag the roll (again, not sealed), and keep it in my crisper.  I can probably get a week out of it this way.
(all times assume you're not buying from a store where it's been sitting on the shelf too long before you buy it; I get my lettuce when I can from the local farmer's market)
So, to answer the specific questions:

keep the bag open; you don't want moisture to condense inside the bag, as it'll make the lettuce rot faster.
I get better storage time with heads of letuce keeping them whole.  If you're going to be eating it all within 2-3 days, it probably doesn't matter, and for loose lettuce, I find it more convenient to wash it as I re-pack it anyway.
You never want to store lettuce wet ... you might be able to store it completely submerged, but damp will lead to it rotting faster.

A:

I have just found the transcript of a Good Eats episode about lettuce storage. It's close to Joe's answer but they say the lettuce should be kept in an air tight bag with air sucked out.
In short they say:

washed 
heads kept intact for delicate lettuce, cut is ok if hearty heads
spinned dry 
wrapped in paper towel
stored in air tight bag with the air sucked out

See senes 9-10-11 of http://www.goodeatsfanpage.com/Season1/Salad/SaladTranscript.htm

