I think the number of people that use private browsing/incognito mode for this purpose makes it obvious that something is needed. Mozilla and google talked a lot about various proposals around "identity" being managed in the browser rather than via websites starting about a year ago.

Mozilla's BrowserID focused more on a really good way of managing a single identity (per Firefox profile), whereas Chrome's MultiProfiles were focused on easily switching between multiple profiles with separate cookies, history, passwords, etc (whether that's for multiple people or a single person with multiple but separate needs online).

Multi-profiles seem good for your need...you can stay signed in with a persistent google cookie in one window (maybe just keeping gmail open), while doing all your regular surfing without the cookie in another window, under a different profile.

Both are still in development though. I don't see multi-profiles in about:flags in chrome, and some poking around shows you might need to run chrome with a command flag, which is a pain. Reviewers seem to like it, though.

edit: it's not a nice integrated browser function, but I guess you could get equivalent functionality by just running different Firefox instances with different profiles. I don't know if there are any problems with that approach, though.

Chrome has a "Open Link in Incognito Window" option.

It seems ironic to use a Google product in order to beat the Google tracking system. I would much more prefer to stay with Firefox in that case.

Chromium is open-source just like Firefox is.