^ +1 above. depends what you want them to do for you. if you want just to go low, actually perform or perform well for track purposes.
there really are dozens of coil-over threads in just the last month. Search and you'll see what people have said about different brands.
OE CSL WHEELS - OE CSL BRAKES - OE AUTOFOLD MIRRORS - CSL TRUNK - CSL DIFFUSER - AA SPORT TUNE - AA PULLEYS - BILSTEIN PSS9s - AS 40% SSK
CF CSL RACE LIP - NAVI - BMW PERF CF STRUT BAR - BMW GROUP N MNTS - GRUPPE M CF INTAKE - UUC SS BRAKELINES, TRANS MNTS, RTABs - 4.10 BMW M-SPORT DIFF