Here's a new version of Dolphin Memory card maker (GCI>Memcard_x.raw) which should actually work. Been working on it on and off and it's much more dynamic, should work. Note that I haven't tested it as I have no GCMs/ISOs.
What it does is allows you to download .GCI saves from say, gamefaqs, and convert them to usable Dolphin Memcards. Just open a .GCI in the program, and click "make dolphin memcard." From there, just overwrite (or make a new one, doesn't matter, though you'll eventually have to overwrite) your old memcard_a.raw or memcard_b.raw file, and run the game. Currently it only supports injecting on a per-file basis (as in, only one game per memcard_x file), but the next version will fix that. Keep in mind that the "data" folder is necessary, and that no other memcard_a.raw will work if placed here (so keep a backup!).
Future versions will be a bit more fancy, such as banner loading, game name recognition (to an extent.. internal names), etc.
Requires .NET framework 2.0.
Edit: Download removed.. undergoing a fix.
Edit 2: Error fixed, tested and works (tested with Wind Waker only, though it'll work with all others theoretically). Source (VB .NET.. uncommented, sorry), and binary are attached.
Edit 3: New version (0.2>0.3). Still haven't received any test reports.. from previous ones, so this is mainly just new features (comment, internal name, and disc serial detection). Also renamed the "data" folder to "dat" so that it can be placed in the same directory as dolphin without trouble. I changed some routines around a bit, so it may also be more accurate (still can't say, I'd be happy if someone would post a report ). These releases may seem stupid, but realize that I'm having to reverse engineer the whole GCN memory card layout from scratch (as Dolphin's are just RAW data), and these are just posted for people to test, and if they work, all the better.
To people who will test: test the app with Wind Waker saves first if possible, then others. If nothing works but Wind Waker, do this:
1) Load the game you're attempting to make a Dolphin save for, have it create a new memcard_a.raw (delete your old one in your dolphindir/data directory)
2) Replace the memcard_a.raw in the "dat" folder included with this program with the file dolphin just made
3) And finally, try the program again. If that works, let me know.