Hotter than hell night
What kind of heat are you talking about? Indian Heat is quite different from Mexican Heat is quite different from Hunan Heat is quite different from Barbecue Heat.
Pick one or two or four, and then I am sure that people will be able to help you out a little bit better.
The hottest food i have ever put in my mouth in this town was some smoked ham dish at Henry's Hunan in Chinatown on Sacramento and Kearny. That hurt, and usually i am pretty good with hot food....but that one was painful.
Good Luck, enjoy your trip.
I am going to dinner with someone I work with and their request was to find somewhere with "good and really spicy food". I think Mexican heat, Chinese or Asian heat, or perhaps some kind of Caribbean or fusion style heat could work. In Boston, where I am from, there is a restaurant called the East Coast Grill, which is a somewhat eclectic mix of styles blending BBQ, Caribbean, and Asian influences with some traditional New England. The food is consistently good and you can always find some very interesting "hotter than hell" entries on the menu.
re: Aaron Lapat
If you'd like Chinese, try Brandy Ho's on Kearny by Broadway in North Beach (not the other branch on Broadway proper). For Thai check out Khan Toke on Geary at 26th Av. in the Richmond for a nice sitdown meal, or if after-bar noodles is more your thing then go to the no-name Thai noodle place on Geary and Leavenworth in the Tenderloin. For Mexican you'd have to travel to the Mission and put up with taquerias. San Jose on Mission and 24th is excellent, as are a bunch of others nearby. Sit-down Mexican in this town is rarely fiery, although I've had good luck persuading the kitchen at Tommy's next door to Khan Toke. Hope you enjoy your trip!