Small suggestion:
I don't know if they exist yet, but I think there should also be "Payment-Request"-QR-Codes.
Like you scan them and get a prompt with a message "Pay 1.337 BTC?" (+value in $/€) and all you have to do is click yes or no.
Only for small amounts though, higher amounts should be typed in manually.
it's already part of the uri scheme (https://en.bitcoin.it/wiki/URI_Scheme). You can put an amount into a bitcoin payment uri.
edit: needless to say you can make a qr-code representing such uri.
side-note: try blockchain.info wallet "create payment request". It allows to enter an amount and produces a qr-code.