hmmm tuff one to answer...
I really like my lever-lock that allows me to lock the front brakes so I don't have to three foot it when stoping on hill climbs and such.
My FI454 has changed my rig a WHOLE bunch too, nice to not have to look for power at higher RPMs cuz the BBC has ALOT right off idel
My upgraded diveshafts are still holding strong too.
Warn HS9500i winch has been a very valuable tool also.