HCl, HNO
3, H
2SO
4, even aqua regia aren't that scary, as basic handling and PPE mitigate most of their risks, and as long as you're near a tap, you can wash even conc stuff off before it does any real damage.
HF (which I've worked with on several occasions... drysuits suck, yo) blows, but in and of itself isn't that hard to handle. It's another acid, and is basically harmless as long as you treat it with respect... it's just that if something does go wrong, it has the potential to go VERY wrong. As a result, the OH&S is extremely tedious; unfortunately this is also the first thing that gets dropped when people get complacent. Let's just say I have seen some shit that would turn a OH&S guy's hair white with terror in some of the labs I've worked in...
DMSO is a tricky one; on it's own is mostly harmless, but if it touches skin it will get into your bloodstream instantly and you'll be able to taste it on your tongue in minutes. Apparently, my old chem lecturers, when they were undergrads, had teachers who would put a drop on a students hand (freshly washed ofc) to demonstrate this (holy OH&S Batman!). The problems though, are that it a) dissolves latex and nitrile gloves (the two laboratory standards), and b) takes whatever dissolves into it with it when it goes through the skin. If the gloves you're wearing had some nasty organic compound on them, you're about to have a very bad day.
The worst commonly used stuff is things like perchloric acid, which can form unstable (think nitroglycerin unstable) explosive compounds on reaction with organic compounds; it is generally used in special fumecupboards because of this. One lecturer was telling me stories about a lab he worked at where, after some renovations, they'd connected the perchloric fume cupboard's chimney to the organic cupboard's... apparently it went boom and blew out the side of the building.
Or refractory metal powders. Self-igniting thermite? Yay.
Although, if we're getting into uncommon... then there's
FOOF.