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RedLaser works well. Really well, actually. I'm not a QR fan, but hey every now and again I do scan one (usually out of some weird curiosity) and RedLaser is the best app for the job.

Opera mini does its job, and approaches QR codes the right way, being an input alternative to the keyboard reachable from the omnibox

Scanbot. Great app for scanning documents, but when you scan a QR code, it handles it.