I wanted the front end of my car to handle better as well as crispen the turning and steering input. One way to do this is to add a strut tower brace available from LLTek. There was a debate whether or not this really does anything or not as the A4 has a double firewall. To end the debate, the S4 has the same double firewall, but it comes with a factory issued strut tower brace. Audi wouldn't have put it on there if it didn't do anything. After I put the strut tower brace and the lower subframe brace on, the front end was noticeably more predictable. Going through corners, especially bumpy corners, the car does not get as upset as it used to. If I get the car to do a 4 wheel drift, the drifting is now more predictable. The front definitely feels tighter.
When you go to install the bar, take a few precautions first. First, loosen the battery clamp and move the battery as far back as it will go. Next, adjust the positive terminal to make sure the power cable and the bar won't touch. In the past, a few people have had problems with this brace rubbing through the power cable and shorting out. This will NOT happen if you take these extra steps. One extra thing I did was to place a thin piece of flexible plastic around the power cable where it comes close to the bar to make sure it would not ever rub through. I did the same where the bar comes close to the ECU main wiring harness. My bar originally was powder coated orange so I decided to spray paint it black. Some parts have the paint chipping off so I may have it redone by powder coating it black. I have successfully run this bar for over a year now with no issues.
Shortly after I put the strut tower brace on, I got the lower subframe brace on the car. On the 99 and earlier model cars, they did not have a brace of any kind. The 99.5 models and up get one from the factory, although it is a bit flimsy. Neuspeed makes a really nice brace, polished aluminum and very sturdy. It bolts up to the transmission mounts and runs across the rear of the subframe. This upgrade was definitely noticeable at the limits of the cars handling. The decrease in chassis flex made drifting the car more predictable at the limit.