Well, I just had one. I decided to take a break from dying every five minutes in Fallout 2 to play me some Fallout 3. What do you know, I get the Firelance event, woohoo! Except.. I can't find the damned thing. I look everywhere in the area for at least an hour. Finally I give up and go home to grab Dogmeat, realize I don't have him on the character I'm playing, and head to the Scrapyard. After all that, I take him back and tell him to find me a weapon. He literally walks two steps and comes back, giving me the Firelance. I couldn't see the $&$&*#%^@$%& thing.
Ugggh, yeah, I hate that crap. The very first time I got the Firelance event, I'm looking around for it near the ruined building near Tenpenny Tower, and give up searching for it after 2 hours, and when I start walking back to Tenpenny to get some ammo and head out, Willy (the water begger outside) comes back, with the durn thing, AND the suit of T-51B power armor which he seemed to have found on Crowley's body, who found the firelance first!
Anyway, on to the list.
Mirelurks
Overlords
Position Reporting Radroaches
Victoria Watts (She scared the living [censored] out of me when she appeared with nothing but her floating hair, eyeballs, and jaw. At 1 o' clock in the morning..... real time....