Probably the most useful ones:
| What | RSS | JSON | HFEED |
|---|---|---|---|
| Everything | RSS | JSON | HFEED |
| Blog | RSS | JSON | |
| Notes | RSS | JSON | |
| Photos | RSS | JSON | |
| Links | RSS | JSON |
Generally, almost every list on the site has an RSS feed generated. For example: for tags, go to /tags/<tagname>/index.xml.
There might also be some secret feeds somewhere that I use for mysterious purposes, but then I can’t go about announcing those can I now?