I've posted a reply to another thread, which I thought I'd copy over here as it is relevant to this thread too:
I haven't done much experimenting yet but I've formulated a few ideas recently. My current idea is to duct/shroud the intake/exhaust air for the CPU to keep it completely separate from the rest of the case (we're talking serious ghetto here, note the "on the cheap" comment on my web page!!
There are a few pictures of my current setup here
and you can see I've already got square cardboard intake duct. I'm planning to replace it with an 80mm round cardboard tube, which should interfere with the case exhaust fan less than the square one.
I'm also planning on constructing a cardboard shroud similar to Spydercat's
(his first one) to exhaust all the CPU air through the PSU. I've already opened up the bottom of the PSU completely just above the CPU (as well as replacing that nasty Titan with a Panaflo) and I've got a temp controlled Panaflo exhausting the PSU. This should keep the internal case temp down, so I can slow the intake and exhaust fans down and still keep the other components cool.
The idea is to separate the cooling into two distinct airflows, so they are not competing with each other: a low airflow going through the case cooling the HDDs, graphics card ane memory etc, and a more concentrated temp controlled (and probably higher) airflow cooling the CPU and PSU.
That's the theory anyway. I'll be reporting my findings back here when I've done this, and see what it does to my PC temps/noise!!