Do a quick search on pod filters, the general consensus is that that blow expensive air flow meters (afm).
Also search for resonsator delete or cold air intake, this is probably the cheapest mod to gain more power safely.
You can follow this how to thanks to qwerty http://homepages.ihug.co.nz/~ccgrant/cai.htm
or I bought one of these parts as I get through a bit of water when on gravel and didn't want to lower my intake
http://www.rallitek.com/hiinel.html.
I also tried these intercooler pipes but didn't notice much difference for the price but it all helps.
http://www.clubsub.org.nz/forum/index.php?topic=2622.msg30987#msg30987
An electronic boost controller is the best way to gain real power if you have a few dollars to spend.
http://www.clubsub.org.nz/forum/index.php/topic,3326.msg43873.html#msg43873
http://www.clubsub.org.nz/forum/index.php/topic,160.msg43657.html#msg43657