The famous blink program but this tiome in assembler.

/*
 * Atmega2560asmtest.asm
 *
 *  Created: 6/1/2015 3:46:37 PM
 *   Author: DarkSector
 */ 



 LDI R16, LOW(RAMEND)
 OUT SPL, R16
 LDI R16, HIGH(RAMEND)
 OUT SPH, R16

;MAIN LABEL
MAIN:  
LDI R16, 0xFF  
OUT DDRB, R16 ;PORTB IS OUTPUT


BACK:  
COM R16 ;COMPLEMENT THE VALUE IN R16  
OUT PORTB, R16 ;PUSH THE VALUE IN R16 TO PORTB  
CALL DELAY  
RJMP BACK ;KEEP DOING THIS INFINITELY

DELAY:  
LDI R17, 100  
LOOP3: LDI R18, 255  
LOOP2: LDI R19, 255  
LOOP1: DEC R19  
BRNE LOOP1 ;KEEP DECREASING R19  
DEC R18  
BRNE LOOP2 ;FOR EVERY DECREASE OF R18 REDO THE PREVIOUS LOOP  
DEC R17  
BRNE LOOP3 ;FOR EVERY DECREASE OF R17 REPEAT PREVIOUS LOOP  
RET        ;RETURN TO PREVIOUS PC ADDRESS  

You can also use the inline assembler directly in Arduino IDE.