Heya,

I've been using notepad++ for coding with byond since forever, and thought that I should probably share what I've learned with others.

N++ has many features which are really handy, especially for larger projects. Here's a select few:
>Tabs (although DM has these now)
>Robust searching: fast RegEx searches; fast Find in Files; search-history. RegEx find-and-replace
>Programmable macros
>Many plugins: collaborative editing (occasionally buggy); spell-checkers; xml-tools; number conversion; syntax-cleaning tools;
>Syntax highlighting: (customizable)
>collapsible comments and braces
>You can SVN right from N++! :)
>compare dm files and have .diff-like highlighting.

I'm not very good with guides or anything, so just point out any bits that aren't very clear.

Here's how my N++ looks:
http://www.byond.com/members/Carnwennan/files/2013-06/ Carnwennan-0001/npp.png

How to set it up:
>Install N++ (I'm not sure whether I'm allowed to post links to other software here, it's a pretty popular open-source tool though so is easy to find)

Setting up a workpane (that bit on the left):
>view-menu->project->project panel1
>drag drop it to where you want
>right click it to add directories to it

Multiple panes:
>drag-drop any tab onto the space where it shows the text. A menu will appear

Regex Searches/Find in Files:
>Ctrl+f will bring up the search menu
>select the find-in-files tab
>select the root folder for your project
>tick "in all sub-folders"
>Set a filter such as *.dm to search only .dm files
>Select whether you want a normal or RegEx search
>Regex guides: http://www.regular-expressions.info/reference.html

Compiling Byond Code from within N++ (kinda):
>open your .dme file in N++
>Run-menu -> Run
>Enter the command 'CMD /K "%PROGRAMFILES%\BYOND\bin\dm.exe" $(FULL_CURRENT_PATH)' without ' quotes.
>Save that command as "Compile Current DME"
>run that command whilst viewing any dme file. It will usually compile in a separate thread! And you can quit the compile at any time.
>You can also compile individual dm files! If you're incredibly lazy and just want run an experiment or something.

Syntax Highlighting:
Either:
>language-menu -> C ... as this is very similar to DM
Or:
>language-menu -> Define your language ... to make your own! You can also set it up so it uses a certain language whenever you open a file with the dm extension.

Hope somebody else finds this useful.

Edit:
Recommended plugins:
>Compare - Used for comparing two files and generating a diffs. Useful when hunting for bugs amongst mountains of copypasta.
>TextFX - Just a bunch of helpful macros...like escaping/unescaping characters.