Depending on how much you want to "raise" it - assuming your springs etc are in good shape, you can order spring pads of differing thicknesses. Part of your lowness may be due to worn spring pads.
First we have to agree "where" we're measuring. I'll use the method we use to do it on Porsches. The measuring tape passing dead center of the wheel caps from the ground to the fender lip.
On my CLK430, I measured this with the OE springs (before Chappy's CLK55 springs went in). The car had 255/40 17 Contis out back and 225/45 Contis up front - rear height was 26.25" front was 26.0"
Low is fine for a race track with no imperfections and speed bumps. The normal street is no place for low. Unless of course you don' t care about the underside of your car.
Where is a good place to get the spring pads of various heights?
To get the height you need do as suggested and add spring pads and adust to suit the eye rather than being too specific with the actuals. If you have a flat floor measure the distance from the floor to the top of the wheel arch as marcusF suggests then simply determine the additional height you would like using the pads. The back are dead simple just one bolt to drop the arm, the front not so easy.
Every CLK left the factory with spring pads. Replacement pads have a Mercedes-Benz part number and are available at the dealer. The last time I checked, pads cost between $3.50 and $4.90 each. There are (or were) 5 different spring pads available. As you've guessed, if you want to increase height, you simply buy a taller spring pad. Aside from the part number, each pad has dots. Without measuring the pads, you can tell which ones you have by checking (feeling) the number of dots your existing pads have. The more dots, the taller the pad. Don't assume that because you have one sized pad in the front, you have the same size in the rear. Maybe you do, but maybe you don't. Here are the part numbers and their height.
A spring compressor will make changing the pads a lot easier. Lastly, your springs may be sagging a little. The fix for that s new springs, which are about $75 per side at the dealer. Absolute lastly, you may want to look at the spring perches. I've never heard of it happening on a W208, but on W124s, W202s, and W210 the perches rust out - which causes A LOT of sag.
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
