BIP 0020

I propose a scheme like this:

() means optional, $* are placeholders

bitcoin:($label@)$address(?$query)(#$message)

Variables

label: Label for that address (e.g. name of receiver)
address: bitcoin address
query: pairs of key=value seperated by &
message: optional message that is shown to the user after scanning the QR code

Query keys

amount: amount of BTC

Examples

Just the address:

bitcoin:18pnDgDYFMAKsHTA3ZqyAi6t8q9ztaWWXt

Address with name:

bitcoin:tcatm@18pnDgDYFMAKsHTA3ZqyAi6t8q9ztaWWXt

Request to send 20.30 BTC to me:

bitcoin:tcatm@18pnDgDYFMAKsHTA3ZqyAi6t8q9ztaWWXt?amount=20.30

Request to send 50 BTC with message:

bitcoin:18pnDgDYFMAKsHTA3ZqyAi6t8q9ztaWWXt?amount=50#Payment%20for%20product%20xyz

Characters must be URI encoded.