I have been researching a bit about the best kind of drop in air filter to get for my Ram. I haven't made up my mind about an intake yet, and if I do get one I will have my buddy that owns a performance shop make me one. He has already told me he wants to do it.
Anyway, I have been hearing for a couple years now that air filters such as K&N (where they are basically oiled gauze/cotton) aren't necessarily the best way to go. While these type of filters give great air flow (at least initially), they are actually bad at stopping the smaller particles of dirt. Not to mention when they become dirty, which will be 80% of the time while in the vehicle between cleanings, their flow rate decreases a great deal.
There are two air filters that are catching my eye at this point.
The Amsoil Ea Air filters look very nice and are the most appealing right now. They use nano fiber technology to catch the smallest of particles yet still flow extremely well. http://www.amsoil.com/storefront/eaa.aspx
They also have them for the 09 Ram. From what I can tell though, it appears as though the same size filter has been used for the Ram (for the 5.7 anyway) since the 2003 model. http://www.amsoil.com/catalog.aspx?code=EAA176-EA
The second is the TrueFlow foam air filters. These are the same filters that are used in the XDi intake which is available for the 09 Ram. They claim their foam filter, while it doesn't flow as much initially, will flow the same even once it gets dirty, plus it doesn't allow anywhere near the amount of dirt through the filter as the oiled gauze filters. http://www.trueflow.com/premiumairfilters.php
Here is a video demonstration of their filter
The filter # for them for the Ram's with the 5.7 is #30201.
So has anybody had any experiences with these two filters? Here is some kind of a test that someone performed on air filters with some interesting results. http://www.roadkill.com/~davet/moto/air.filters.html