A couple more I find useful:

- Evernote Web Clipper - for saving code snippets and notes about projects - Resize Window - to open a page in a resolution of your choice. Very useful. - Awesome Screenshot - take a screenshot and let people know what you think about a page ... if you're using Safari, Coda Notes is much nicer, though :)

And, of course, the developer tools included in Chrome (first in Safari ... and they still are nicer there) are great, too.

Any more extensions HN users find useful?