Diigo does this for free. You can bookmark the page, save a cached copy and optionally annotate the page as well. They have browser plugins for Firefox and probably IE and a JavaScript bookmarklet that works with Chrome and Safari etc.
I just checked out Diigo and it looks pretty cool. It lets you annotate, share, and search your archived bookmarks which as far as I can tell, Pinboard doesn't do.
On the other hand, Diigo only stores the HTML (like wget) and a screenshot, whereas Pinboard will store the CSS, Javascript, images, and embedded videos, similar to what right-click, Save As would do (minus the video?).
