Thought of a few more...
A room with a closed, locked door. The PCs can hear something, very faint, through the door. If the listen at the door, without specifically stating that they are protecting their ears in some way, as soon as they put their ear to the door an Ear Seeker (or whatever they are called these days in 3.5e) burrows into their ear.
A stone statue of an attractive, winged, female with wings. On the base of the statue is a word written in a strange language. The word is the name of the demon represented by the sculpture, and if someone says the word aloud, the demon is immediatly summoned and attacks the party.
Trolls. You must have at least 2 trolls whose limbs get severed and continue to crawl towards the party.
A magic, intelligent sword who talks aloud to the party, maybe even sings, and is itching for a fight. He calls out for something to kill, and if drawn during an encounter, he will challenge the biggest monster to a fight. He continually calls out things like "Yes! Go get him! We can take him! Come here you big ugly thing! Wanna piece of me?" Even when put away, he will keep on talking, making it very difficult, if not impossible, for the party to move quietly. Of course, its very difficult not to use him, as he is something like a +3 Flaming Longsword who can grant the wielder the ability to become invisible 1x day.
