Between me and my brother we broke quite a few bits, mainly from them failing rather than crashing or bad maintenance. List that I can remember:
Numerous shimano BB's (only one that lived was a hope titanium)
Hope superlight front hub (got the replacement still in box!)
Shimano hubs, orig XTR, DX, XT, STX
Rims - campag, ritchey
Spin front wheel - through the rim (was a crash though!)
Frames - Giant ATX, coyote, USA raleigh, Specialized FSR
RST Hi 5 forks - twice, once just destroyed all the internal components with no external damage
Rapidfire units (lots!!)
Cannondale Headshock
Hope rear freehub
A couple of saddles
Azonic tripple wall handle bars (brother bent them up!)
Pedals - Onza HO's, Shimano spd, black widows - bent axles jumping over a wall - he then made new titanium axles in what remained of the lunch break!
Rockshox front forks, judy's, mag21's
Have seen broken - intense M1 frames, sunn radical plus, very abused coella and lots more.
Out of all the things though the most impressive was my brother and his friend managed to put a crack in a Scott LSD WC - the original many adjust one. It became the only frame the two of them would trust, took so much abuse that I don't think anything else would have stood a chance! His one is sitting in my dining room at the moment being rebuilt with Hanebrinks.
Components that we have been very impressed with:
Original XTR cranks
Thumbshifters - even landed the bike on them one day and they still work!
Cannondale Super V - bent a set of tripple clamps on it with no effect on the frame
Scott LSD frame
Hope Ti bottom bracket
Hope Hubs - even if we broke them their service was superb and without question
Rhyno Lite rims
That's all I can remember for now!
Ed