Here's a few things on my list:
Harmonic Balancer (ATI or other improved aftermarket, if available)
Cup holder (51168217953 or eurotray 51167038323?)
Center console (51168218305)
floor mats (82111470424)
A-pillar (51437902933 and 51437902934)
Billsteins - coilovers such as PSS, PSS10, or I'd consider replacment shocks/struts too
Turner or H&R Sways
M3 motor mounts
M3 transmission mounts
M3 Driveshaft Guibo
GSR 4-bolt oil pump shaft (http://store.bimmerworld.com/gsr-m52...aft-p2210.aspx)
INA Over Running Alternator Pulley (022 903119C?)