Those things that you need to buy every now and again which are not much to get excited about.
I’ll start with the bottom bracket. Compared to say a new XT mech, an XT bottom bracket isn’t anything to get too excited about. You don’t see it, and what you can see of it are just 2 little bands of metal at the bottom of your bike. It just sits there doing its job with little attention. No fancy moving parts, just a couple of bearings. Apart from fancy ceramic bearings, some nice colouring, machining and seals there’s not much more you can do to a BB to sex them up.
Any others? Please let me know what else you think is a dull, and often under-rated component, maybe we’ll try and find some exciting aspects about them along the way.