Yahoo! Finance with little to no fanfare. Above the charts on the individual stock pages and on Yahoo Finance's front page you will see . Click the "On" button provides a drop down display of streaming stock price information. Click on the "?" and learn that you can leave this open for up to 25 minutes and although these are streaming, they are not "real-time". They are delayed 15 minutes.
Streaming quotes has only been offered with real-time information as part of a Yahoo Finance premium service package.