Greenleaf just posted their new glassware on APC, and after visiting their site, it looks tempting, especially for people with larger tanks. I know on my 80gal, I really cant count how many bubbles actually pass per second, and with a 120gal on its way, I know it'll be worse.
http://www.greenleafaquariums.com/co2-bubble-counters/cal-double-counter.html
http://www.greenleafaquariums.com/co2-bubble-counters/cal-double-counter.html