These are the official IRC channels on irc.caffie.net sponsored by SMWC.
For those who want to focus mainly on Super Mario World hacking, there is another, somewhat less popular channel, #serioushax, which is also hosted on irc.caffie.net. In this channel, conversations can be random, but are often about things such as ASM. It's possible to talk about general ROM hacking or homebrew ROMs in this channel, but keep in mind that most people in the channel only know 65c816 ASM.
Founded by Roy in August 2008 and technically not an official channel, but often regarded as one.
#imamusic is the successor to the now-defunct channels #lolmusic and #smwmusic. The channel is home to many of SMWC's music porters and people can go there to discuss porting, get feedback on their ports, request help, etc.
There is also a channel set up specifically for this wiki. The goal is to keep wiki chat out of #smwc and #serioushax. The channel has been changed to #smwiki.