sound
If you haven't utilised it yet then do so! I was blown away (almost literally) when I installed a subwoofer system under my seat. The greater immersion factor was astounding. You really shouldn't be without it even for the most moderate of sims.
I had been thinking about it from the start, but was on the lookout for some suitable and cheap speakers or bass shakers. I found fairly inexpensive bass shakers at Jaycar Electronics but then while walking the dog one afternoon I stumbled on a neighbour who was throwing out two 15" subwoofers on his front verge!! I promptly got the car and transported them home. I had a spare Creative 2.1 speaker amp that I thought might be powerful enough to drive them and to my surprise it did. While only 25 watts max power, it does a fantastic job!
The other thing that might be required is some tweaking of the sound file for individual aircraft. Some are better than other off the shelf. I found PMDG aircraft have great sub sounds straight out of the box, whereas others are a little unrealistic, so a knowledge of FS sound config parameters could be handy. I don't have, so FS Sound Studio might be the go for me.
Anyway enough rambling, here's some pics to explain. Unfortunately I can't demonstrate the bass sound, so you'll just have to try it for yourself.
This is one of the two 15" Sub Woofers I picked up. This one is in good condition but the other has some damage on the speaker webbing, however I don't want great fidelity out of it, just great shaking, and it does that just fine.
As you can see I had to modify my seat base to accommodate the large diameter speaker. It only just fits too as the speaker magnet is resting on the floor, but I suspect this may be adding to the vibration factor.
Fits nicely under the seat and I managed to get the 25W Creative sub amp in the seat base as well. I took the subwoofer output of my Audigy sound card and sent it to the amp and added a simple on/off switch. I does rattle the seat springs a little during extreme sounds though.
These are 4 ohm speakers and the subwoofer connection on this amp is also min of 4 ohm, so the second speaker installed in the co-pilots seat will be connected in series (total of 8 ohm) to avoid overdriving the amp output. The amp is powered by a 9v external power pack.

