Now that the monsters are leaving the "suitable for a level 1 party" range, their powers start to grow more unique and varied. These are some of the guys that, with a little reskin, can be dropped into any SOP marauding orc tribe or undead shambling horde. I'll offer reskinning suggestions at the end of each entry.
This monster is all kinds of fun, mostly because if you can sit him behind cover and roll a stealth check to hide again, you can simply announce to the players that they now (seemingly inexplicably) grant Combat Advantage or are now more susceptible to the undead brute's attacks. Be sure to play up cover and concealment in this encounter and have lots of shadowy corners, some with movement that turn out to be harmless rats, and some with Devourer Initiates in them. These guys work great as ringleaders or minor necromancers to harass a party, and are Artillery that also act like leader-controllers. Comboing them with skirmishers makes for a lethal encounter due to their CA-granting at-will.
Devourer Initiates are in Dragon Magazine 371, the article about Acererak.
Angry Mobs are a good way to spice up the average city encounter. Say the party's just got in to town, with a bunch of low-level items to pawn off. But they've gained the eye of the king's vizier, who secretly summons a big nasty monster or two in the middle of the market district to take out the party. Now while they're fighting the monster, they have to simultaneously use Acrobatics/Athletics/cover to stay out of the way of a rampaging Angry Mob. This monster is best represented by a clear plastic cel moved around on the battle mat, since it doesn't have the same way of moving as a normal gargantuan creature. This also encourages the party to describe their "subdual damage" hits, since it's likely they don't want to actually kill the Angry Mob, simply disperse it. You could easily have the Mob break up when it hits bloodied, or allow skill checks of Intimidate/Diplomacy to deal damage as if they were attacks. But if you reskin this as Orc cannon fodder being forced into marching as a line of spearmen, this is a great, brutal monster that actually acts more like terrain, since the orc leaders (full monsters) are free to move about in it, while the party has to either step out and use ranged attacks or find some other way to break up the Mob. Again, as "spearman cannon fodder" the idea of the mob breaking in two or shrinking when bloodied offers a tangible reward for players dealing with the threat. Angry Mobs are in Dragon Magazine Annual 1.
Good ol' Wraiths! Wraiths are a great add-on to any fight, assuming you set it up right. Keep in mind their movement speed of "Fly 6 (hover), Phasing" and abuse both of those. Wraiths are completely insane negative-energy beings, but they aren't mindless. If you set up an encounter in, say, an old library, now you have rows of musty bookshelves that create blocking terrain the wraiths can pass through without difficulty (and pass back through to end line-of-effect), and wraiths are more than happy to fly up out of combat (and stealth into some shadows in the ceiling) to regenerate for a turn or two before entering combat, and because of their "insubstantial" attribute, they basically have paragon-tier regeneration. Be sure to give the players ample opportunity to get around these wraith tactics, such as Athletics to domino-topple the bookshelves, making it all difficult terrain instead of rows of blocking. Between their weakening attack, Insubstantial, Regeneration and their ability to leave combat, Wraiths can be a bit of a slog, so you do want to offer the party some in-arena ways to counteract them. It could be something like an Arcana/Religion check to notice a particularly holy book that the wizard could then spend minor actions wrapping pages of around the Ranger's arrows to make them deal Radiant damage, or a cistern of Holy Water nearby, but if the party has a battle/pacifist cleric with no Turn Undead for some reason, know that Wraiths can be incredibly annoying. They're also in the Monster Manual.
Zombie of Iuz
Located in the obsure RPGA: Return to the Moathouse module, the Zombie of Iuz is just a well-put together minion. They tend to bunch up around whatever's closest, grabbing and imposing attack/defense penalties, thus making future grabs easier, and if the wizard lights up the gang around the defender, they have a final "kiss off" explosion for a little necrotic damage. They're far more compelling foes that normal shamblers, because they have three powers that all work well together and give a 'damned if you do, damned if you don't' effect. They also can make skirmishing PCs like Rogues very, very unhappy, but they give the defender something to do (go over and defend the rogue), so they're interactive. Comboing them with some sort of lurker that attacks the party's controller can make for an absolutely brutal fight, with no ranged crowd control options to shake off Zombies of Iuz.