Browser which always allows scale/zoom? I absolutely 100% hate, hate, hate mobile-optimized design sites, particularly ones that disable zooming. Up until now, I've done pretty well spoofing a desktop user agent to get the full pages, but with the advent of responsive design, it seems like more and more sites are feeling comfortable using viewport meta-tags to set user-scalable to false, which means that I am in effect forced into using the horrible mobile sites. 

From what I understand, viewport tags are ignored by desktop browsers - is there a browser on Android which does the same thing, preventing web sites from removing key functionality from my phone? Maybe a Dolphin add-on? 

I think potentially a greasemonkey script excising the offending viewport tags would also work, but I'm not sure there's a stable version of greasemonkey for android yet, and it might be preferable if the browser itself were built to always allow zooming.
Just found the setting in Chrome.  If you go to Settings -> Accessibility and then tick the option "Force enable zoom" then you should be able to zoom in on any site.  (I have read a few sites still manage to stop you, but the vast majority should then work).