A greddy Type S is probably on of the most popular BOV's used(if you havent noticed from its support on this thread). Another interesting one is the new APEXi twin chamber sequential. Using 2 chambers allows it to equallize internal and external piping pressures, creating less turbolag by not completely evacuating the charge pipe. Some rally cars do this by using a Recirculating valve hybrid to keep charge pipe pressures up, makes for some wicked quick spools between shifts. Also, the Turbo XS RFL is a very loud BOV. like 110+ decibles at .45bar or something. Just absolutely terrifying. A good friend of mine ran an RFL turbo-intercooler side of his piping and a Greddy on the Charge pipe side to really regulate pressure(somewhat overkill, but super effective). The sound was kind of a FOOOOOOOOOOOOOOOSSSSSHHHHHH followed quickly by another smaller foosh and a loud highpitched wistle. And this was just driving normally. It sounded like a canon or something when he raced, just a nice loud booming discharge of air back to the atmosphere.