I saw a thread about one on acmlm years and years ago... it was kinda awesome   Don't remember which version of acmlm it was though...

Hmm... But that's not a hack, but some sort of emulator add-on... Or something... Should still work if you're using FCEU...

There are patches for an in-game mini-map as well as for a wall-jump feature, both made by Parasyte. (Around the time he made these, he was working on a very impressive-looking hack called Metroid: Ruins. Shame it was never completed*...)

I happened to have these two patches stowed in the depths of my drive from a time when I briefly dabbled in Metroid hacking. They can be gotten at http://members.fortunecity.com/grond1911/metroid.html for the time being.

Personally, I don't like the default usage of the 'empty energy tank' graphic for the empty spaces on the mini-map... however you can make it use blank tiles instead by hex-editing ROM offset $1CA7D from 6E to 6D after patching (in an otherwise-unhacked Metroid; some hacks may use tile 6D for new graphics.)
The tile used for rooms can also be changed, at $1CA79.

The Acmlm Board thread where both of these were originally posted (most certainly the thread Celice was referring to):
http://acmlm.kafuka.org/archive2/thread.php?id=3483
Unfortunately the screens of Metroid: Ruins linked to in the thread don't even seem to be in the Wayback Machine, so I fear they have vanished from the net

*A small thread wherein Parasyte gives his reasons for not finishing MR:
http://acmlm.no-ip.org/archive2/thread.php?id=11348

EDIT:
Forgot to mention that yes, these two patches can be used together--just make sure to apply the map patch first and the walljump patch after.

Thank you all, it was indeed Parasyte's hack!

As for the Lua add-on, that is amazing, I'm going to compile fceux and try that out too.

Thanks again!

P.S. Sort of beyond General Romhacking, but it would be nice if these were added to romhacking.net.
Would permission from the author be needed, from the readme:

     Can I use this patch in my hack?
     --------------------------------
       You certainly can! Just apply the ips patch over your hacked ROM, and have
     fun with it. All I ask in return is that I'm given credit for the AutoMap in
     your readme, in the ROM, or both. Take your pick.
     You are also free to modify the AutoMap source code however you see fit, with
     just one exception: the copyright notice may not be changed or removed.
     Everything else is open to change."

It doesn't specify much about distribution of the patches and asm source, but it would be a big loss to have this fade into obscurity.

The map patch is pretty awesome. I never knew anything like this existed. It's kind of self-defeating, though. Metroid's rooms are so densely-packed together that your mini-map is not going indicate anything useful. It's still a cool concept, none-the-less.

Perhaps if the mini-map were larger and could indicate some kind of markers, (bosses, pick-ups) it would be more practical.

I played around with this a little bit more, and it's actually a trivial matter to increase the area shown by the map. The main problem is the graphical glitches that occur due the extra sprites being drawn to the screen. But pushing the map up to a 4x4 grid seems to work okay, at least in the few minutes I playtested it. Try it out by making these changes to the patched ROM:

$1CA63: 03 -> 04
$1CA9B: 03 -> 04
$1CAC4: 12 -> 16

Celice, there are a few screens of FFC availiable at this link: http://web.archive.org/web/20040609102642/http://challenges.cg-games.net/ffc/
Most of the pictures weren't archived though, it seems (at least I could only get 8 of them to load in the screenshots page).