It's pretty hard to beat the factory cones and shock setup. A new set of rubber cones and a good quality set of shocks will give a really good ride, and will be height adjustable with a set of Hi-Los. The rubber cones will degrade over time and a new set of cones will make a huge difference over old ones.
Rubber cones:
http://www.minispares.com/product/Class ... M3968.aspxOr the hard "Red Spot" cones
http://www.minispares.com/product/Class ... TR687.aspxHi-Los:
http://www.minispares.com/product/Class ... O-SET.aspxThe next option they sell is the drop in coil springs, which replace the cones. I've never tried a set, but I have heard mixed reviews (like them snapping).
http://www.minispares.com/product/Class ... RP100.aspxThe last option is the coil over kits. They bolt onto the shock mounts, which means that you're supporting the entire weight of the car on the shock mounts. This can mean you get failures of the pins on the suspension arms as well as the body mounts.
http://www.minispares.com/product/Class ... SX519.aspx