This one works very well for me.
I have a product called the Drop Stop in both my cars.
Works great.
I found the horn to be way too wimpy so I replaced the stock one with this PIAA pair.
I also didn't want to screw my plates straight through the front bumper or directly against the back bumper so I put on license plate brackets that I think make it look much nicer.
I took the advice from a bunch of folks on the subaruoutback.org forums and put in a new 19mm sway bar. It was a pretty easy install, but honestly I can't tell if the drive is better or it's just a placebo effect.
Then just a couple of simple quality of life things just because:
I got these from Amazon. They were great!
The ones with pockets don't hold in the space well, and fall down, but you can still get to your stuff if it falls. I put them under these for hidden space.