Muffler bearings, blinker fluid and piston return springs.
I’ve tried really hard to only post stuff I’ve actually done and not just link to some website, but this one deserves a link. Kale Auto has some very hard to find auto parts. While many have searched in vain for a quality replacement muffler bearing, Kale has them for only $49.99 a piece. They also carry high performance parts, for instance, why stop at crossdrilled brake rotors when you can also get crossdrilled brake lines. And everyone needs an adjustable power band.
I posted some of these links over on Metafilter, and in the comments many people brought up similar products for other trades, like drywall expanders for builders, prop wash in 5 gallon buckets for aircraft, etc. Its worth a read.
