I currently have a mixed set of Monroe Sensatrac (front) and Gabriel Premium VST (rear) shocks. What I have learned through the years is that shocks, more than any other suspension component, affect how a car feels on the road. If you think your springs are too stiff, disconnect the shocks and then test the suspension. Most likely you will be surprised. Moreover, it is the rebound stiffness in a shock that makes the most difference. The idea is to have the softest suspension possible without compromising the suspension's ability to apply the tires to the road in the most consistent way. How stiff or soft a suspension should be depends on many things such as: the geometry of the suspension particularly at the extremes in range of motion, the ride height of the vehicle, the vehicle speed at which it should perform the best, the amount of weight transfer like in drag racing or balance like in road racing, the amount of road feel desired by the driver and the quality of the road it is designed to drive on like bumpy or smooth / wet or dry etc. Here is my rating of different shock models based primarily on two cars; my 1985 Rx7 and this 1992 Camaro. Both of these cars have seen action at the race track and on the street.
KYB makes an inexpensive nitrogen gas performance shock. I have used them on both cars mentioned with equal results. They have a life time warranty and appear to be of good construction. One should be aware that these are performance shocks which have a very high dampening rate. This will make for a stiff ride but better handling, cornering power and feel on the race track. In my opinion cornering power is lost on the street because they cannot cope with the bumps on the average urban street (and neither will your back).
A good replacement Heavy Duty shock would be a Monroe Sensatrac shock. The front strut cartridges provide a firm ride but don't compromise comfort for the street. I believe these are valved better than the KYBs. The rear Sensatrac shocks have heavy rebound dialed in but they are not as firm as the KYBs. Though they handle well on the street, I consider the rear Sensatracs to be uncomfortable.
Gabriel makes a Heavy Duty unit as well. They are very inexpensive at about $12 each and have HD valving comparable to the rear Sensatracs. Gabriel also makes a Premium VST shock at a whole $19. The rebound and compression are almost equal and the ride is comfortable but firm and matches well with the front Monroe Sensatracs. I have not tried the Premium VST in the front.
Someone dedicated to the best money can buy should go for the Koni or Tokico adjustable units. They should give every possibility at the twist of a knob.
Installation can be done with hand tools. The front wheels will need to be removed for access. In the rear, carpeting must be pulled back to gain access to the upper bolts. The car will need an alignment after installation. Replacement of shocks will also improve brake response as the car will have less of a tendency to dive under braking.
Gabriel http://www.gabriel.com
KYB Corporation www.kyb.com
Koni http://www.koni.com
Monroe http://www.monroe.com
Tokico http://www.tokico.net