Guess the rest of the message didn't make it through. I've seen some that can 1 or two shot you in full iron armor. They occur at level 40 and below to make subsurface exploration a little more exciting. Just a thought.
We had a bunch of real dangerous things in the overworld, but most got moved to the nether due to complaints. we could create some new dangers for sure though. One of the things I wanted to do was have a mob creation contest and the best ones that won could be named by the players.
If i get some time I might try to submit to that. I'm not sure I want as much danger as Fdrandel, though. I play minecraft to build, not to get ganked. I like the orcs/inferno spiders being kinda the top of what we see on main. I think the nether wraiths are basically on target, but they do too much harm to the armor. I could literally burn a whole set of veteran armor before i hunt enough wraiths for then to drop another set. The one wraith mob I object to is the exploder. There's no way to un-trigger him like a creeper, and he's immune to arrows, so you can really never actually kill him and see his loot table. The purple mobs in the nether are pretty good, but the blood witch's healing makes her a long, boring fight. The skeletal dark knights are a bit ridiculous. Even in full veteran they can waste three bars of hearts in about 2-3 hits. Finally, if I had to get rid of one mob it would be the huge nether slime. They are annoying, lack a good loot table, and take far too long to dispose of since they divide about ten times before finally dying.