I am in the process of developing a payment system for Bitcoin. The intention is not to be a rival for systems like bit-pay, instead I am focusing on transactions that provide immediate feedback to the user without even having to change page on the site.
Bit-pay actually does this today. It provides a notification to the user the moment the transaction is received (usually within a few seconds of sending). You get a little yellow popup box in the lower right of the page informing you that payment has been received and giving you a link to click to refresh the page. I chose not to automatically refresh the page because I think that would be a rather invasive and disrupting user experience.