As I do some microcontroller-programming in assembler and like to use powerful editors I set up some modes for jed (an editor available for linux (console/X11), dos and windows). It can behave like emacs (or some other editor if you want to) and supports useful things like folding. There's a place on the web where you should find lots of modes for jed: the jed modes repository.

My modes are quite well to work with--just test them if you like. Syntax-highlighting is included (it may be that I've missed some instructions) as well as some automatic indentation, which works pretty well.

To use them, copy the files to your jed/lib/-directory and insert the following into your .jedrc:

% 
autoload("pasm_mode", "pasmmode");
add_mode_for_extension("pasm","asm");
% 
autoload("a51_mode", "a51mode");
add_mode_for_extension("a51","a51");
% 
autoload("avr_mode", "avrmode");
add_mode_for_extension("avr","avr");
% 
autoload("tdsp_mode", "tdspmode");
add_mode_for_extension("tdsp","tia");
%
autoload("c166asm_mode", "c166asmmode");
add_mode_for_extension("c166asm","asm");

Additionally use a first line in your files which tells jed what they are:

; -*- mode: avrmode; mode: fold -*-
; -*- mode: pasmmode; mode: fold -*-
; -*- mode: tdspmode; mode: fold -*-
; -*- mode: a51mode; mode: fold -*-
; -*- mode: c166asmmode; mode: fold -*-

8051-Assembler (4479 Byte) (Version of 26.06.2001)

Microchip-PIC-Assembler (16X8X) (4764 Byte) (Version of 18.07.1999)

Texas Instruments TMS320-Assembler (6430 Byte) (Version of 24.01.2000)

Atmel AVR-Assembler (10163 Byte) (Version of 19.01.2006)

c166-Assembler (6065 Byte) (Version of 26.06.2001)