ROM hacking communities
There are a number of ROM hacking communities, many focused on a particular game or series. Below is a brief description and a link to a number of hacking communities. Romhacking.net also maintains a database of links to relevant web sites.
SMW Central is a place for all things related to Super Mario World hacking, as well as other Super Mario games.
Metroid Construction is home for any and all Metroid hacking, though Super Metroid receives the most attention by far. The site contains hacks, utilities, documents, and lots of discussion and active members.
Anyone can feel free to move any of the following sites to its own section to expand upon the information provided.