1- HD Textures [10/8/15] (for ISO and SD)
- Official thread by Yami 2b (Updated as of 8/24/15)

Gallery

Instructions:

1-   Download and extract the HD pack (4.0.3).  
     Optimized [DDS] - Mirror (Recommended)
     Normal [PNG] - Mirror (In case DDS doesn't work)
2-  Rename the _rename folder to RSBEF2 (for netplay ISO) or 00000000 (for the new SD method)
3-  Move the RSBEF2 or 00000000 folder to the custom textures load folder:

Possible locations:
       Global config (Most cases): Documents/Dolphin Emulator/Load/Textures
        Portable (if there's a portable.txt file in the same folder as Dolphin.exe): <Dolphin Installation folder>User/Load/Textures 
4 -  Enable custom textures in Dolphin > Graphics > Advanced tab
5-  IF it still doesn't work, try moving the Texture cache accuracy to Safe. However, this will probably slow down the game significantly!

Notes:
- You need a good PC/Mac for this, since the point is to play it at high resolution. How good? You should be able to play the game in Auto (Window size) or other high resolutions.
- If you have a fast PC and hopefully SSD, but want to get rid of some stuttering in-game, check "Prefetch Custom Textures" so that it loads all textures before starting the game. Might increase game start time, though.
- This pack does NOT cause desyncs. poor connections and config mismatch (like turning on Memory cards, SD Card and Wiimotes) might, though.
- DDS format  is optimized to be loaded in memory a lot faster. Here's a comparison of the performance (Using prefetch at startup): PNG (Normal) vs. DDS (Optimized)

2- Shaders (Post-Processing)
- DolphinFX thread by Asmodean

Comparison (Blended Bloom):
Character Selection Screen + DolphinFX
Saffron City + DolphinFX
Battlefield + DolphinFX

 1- Download DolphinFX.
 2- Extract it.
 3- Move DolphinFX.glsl to the Custom shaders folder.
     Location:
     Global config: Documents/Dolphin Emulator/Shaders
     Portable (if there's a portable.txt file in the same folder as Dolphin.exe): <Dolphin Installation path>User/Shaders
4- Go to Graphics > General and select OpenGL backend for graphics.
5- Go to Graphics > Enhancements and select DolphinFX for the Post-Processing Effect.
6- Click Config next to it and tweak the settings as you like (can be done in-game). 

Notes:
- There are many effects you can try, but my favorite is Blended Bloom because the lighting looks smoother. These are the settings I'm using. YOUR taste will probably vary, so tweak according to your own preference.

3- Brawl / Project M playable soundtrack (Now with MP3 output support) [8/19/15]

For Brawl

 1- Download and extract BRSTM Converter.
 2- Download and Install Bulk Rename Utility.
 3- Download the Brawl batch rename pairs text file.
 4- Open Dolphin, click Smash Bros. Brawl > Properties > File System and Right-click Partition 1 >sound > strm and click Extract Directory... and save the files somewhere.
 5- Open Bulk Rename Utility and click File > Import Rename-Pairs and open the downloaded text file.
 6- Navigate to the extracted folder and select all from the list (Ctrl + A).
 7- Click Rename (at the bottom right) and confirm the changes.
 8- Open BRSTM Converter and select an output format (I recommend MP3 or Ogg for smaller size, but Flac has better quality)
 9- Uncheck "Show SoX" (this will hide the bunch of window pop-ups) 
10- Click OK and navigate to the folder with the files you extracted and renamed , then select all (Ctrl + A) and click OK.
11- KEEP CALM AND WAIT ON

 For Project M

 1- Download and extract BRSTM Converter.
 2- Download and Install Bulk Rename Utility.
 3- Download the Project M 3.6b batch rename pairs text file.
 4- Open Dolphin, click Smash Bros. Brawl > Properties > File System and Right-click Partition 1 >sound > strm and click Extract Directory... and save the files somewhere.
 5- Open Bulk Rename Utility and click File > Import Rename-Pairs and open the downloaded text file.
 6- Navigate to the extracted folder and select all from the list (Ctrl + A).
 7- Click Rename (at the bottom right) and confirm the changes.
 8- Open BRSTM Converter and select an output format (I recommend MP3 or Ogg for smaller size, but Flac has better quality)
9- Uncheck "Show SoX" (this will hide the bunch of window pop-ups) 
10- Click OK and navigate to the folder with the files you extracted and renamed , then select all (Ctrl + A) and click OK.
11- KEEP CALM AND WAIT ON

4- Brawl Revision 2 Downgrade (For netplay builders)
- Official thread by /u/Rukario

Are you one of the few people who actually ripped their own Brawl discs for netplay but it was Revision 2, which desyncs with most people? Keep readin'

 1- Download the XDelta Brawl Revision 2 downgrader
 2- Open xdelta\xdeltaUI.exe
 3- Make sure you're on the Apply Patch tab and use the following settings:
     Patch: open "Revision 1.xdelta" (inside the Revision 2 Downgrade folder)
     Source File: <Your current (hopefully ripped) Brawl ISO revision 2>
     Output File: <Output file name>.iso
 4- Click Patch and WAIT for the success notification. (Program might take LONG and look UNRESPONSIVE, so just give it time to finish, like 10 mins)
 5- Verify the file and make sure the MD5 matches: d18726e6dfdc8bdbdad540b561051087. Can be done these two ways:
     A- Use Dolphin > Right click game > Properties > Info tab > MD5 Checksum compute
     B- Use WinMD5, which comes inside the Project M builder's winmd5free folder.
 6- Voilá! The ISO is now ready to be used to build netplay compatible mods like Project M.

5- Virtual SD Card mods for offline play

Ever wanted to play BrawlEx (100 characters), ASL (alternate stages) or any other kind of SD card-exclusive mod? This is how:

 1- Download the pre-configured Dolphin for SD Card (Portable, its config will be independent to your current Dolphin).
(You can use your current Dolphin, but this is to avoid forgetting to turn SD card off for netplay)
 2- Download Gecko.
 3- Get a virtual SD card with the mod files:
     A- Download the pre-made Dolphin SD Card of your choice. (Needs to be made with WinImage, not ImDisk)
     B- Make your own virtual SD card with the mod files. Guide
4- Move the extracted sd.raw file to <Dolphin folder>/User/Wii 
5- Add your games folder and set your Brawl ISO as default through the right-click drop-down menu.
6- Open the Gecko (.elf) file with dolphin and press A to start the mod

+ 

6- Virtual SD Card mods for netplay (OUTDATED)
- Official thread by /u/Rukario

Ever wanted to play BrawlEx (100 characters), ASL (alternate stages) or any other kind of SD card-exclusive mod via netplay? This is how:

 1- Download the pre-configured Dolphin for SD Card Netplay (Portable, its config will be independent to your current Dolphin).
 2- Open it and configure Controllers, Game path(s), Graphics (resolution, anti-aliasing and texture filtering) and netplay nickname.
 3- Get a virtual SD card with the mod files:
     A- Download the pre-made Dolphin SD Card of your choice (Recommended, needs to be made with ImDisk, not WinImage). Check my SD card mods vault
     B- Make your own virtual SD card with the mod files, upload it and share it to avoid desyncs. Guide.
 4- Move the extracted sd.raw file to <Dolphin folder>/User/Wii
 5- Start a netplay lobby with Brawl (yes,  RSBE01 Rev 1)
 6- Make a save file (Select Yes or just press A), go to stage builder and delete the 3 current stages
 7- Exit Stage builder and go back in
 8- Voilá! Gecko should load and just press A to start the modded game!