I killed my party of 5 first level characters with:
2 fire beetles, 2 goblin skirmishers, 1 goblin blackblade. Cleric went down due to a crit/fire blast from the beetle. AFter that it was just chipping away. Only one character survived so I mulligan'd that to allow them to keep going:
The next fight was against a goblin hexer, 1 sharpshooter, 1 goblin skull cleaver and 4 minions. This one would have gone better had the rogue and wizard NOT ran off the other direction planning on some sort of surprise attack, leaving the cleric and fighter to be beaten to a pulp while the warlock kept missing with his eldritch blast.
They were captured (technically killed but, again, I didn't really want to start a new game).
Fast forward a few weeks. They're now 3rd level with plenty of magic items (following the parcel system, each character had a magic weapon/implements and some had armor. The party had about 2 pot's of healing each.
The encounter 1 ettercap webspinner, 2 fang guards, 2 deathjump spiders. I wanted a somewhat challenging encounter, so I went with this level 4 suggestion in the book.
In round one, the fighter was poisoned and immobilized, and the cleric was immobilized. The wizard was firing magic missiles from the back, and the warlock was trying to hit with an eldritch blast. (the rogue was absent) In round two, the cleric became poisoned and the webspinner shot his web out to ensure immobilization on the cleric (who made his save).
round 2
A spider jumped and attacked the warlock, but missed. The warlock used his teleport power to hit and immobilize the 1 spider. The wizard used magic missile on a fang guard and hit. The cleric missed with both his daily and hit with one encounter power (used an action point) and the fighter hit hard with one of his encounters. The ettercap fang guard was nearly dead, but knocked back due to the cleric attack
round 3
The wizard used his fire shroud to hit the webspinner, but missed the spider. He was too far away (and didn't move) to hit anyone the fighter & cleric were fighting. The warlock used his eladrin teleport to move out to the open and attacked the spider flanking the fighter, but missed. The ettercap fang guards moved in and took out the fighter, leaving the cleric still immobilized. The spider then jumped to hit the warlock, critted and took him out of the fight. The webspinner moved up, restrained and poisoned the wizard.
Round four, the cleric healed the fighter and killed one ettercap, but he went back down from a crit with a greataxe from the remaining ettercap. The other spider then jumped at the cleric and hit, taking him down.
The wizard was the only one still up, but he only had 3 hp and was poisoned. he went down at the beginning of round 5.
So, yeah, it's been quite deadly. I'm taking a break from DM'ing to read up some more, cuz maybe I'm too deadly.. I dunno. I'll be playing a rogue in one of the other guy's games for a while.