Noel Borthwick [Cakewalk]
If you have the Waves suite you get around 600 plugins just from there :)
FWIW I've tested with over 1000 plugins and SONAR still does the startup scan in less than 5 seconds for me.
My systems lists about 800+ due to WAVES, NI and others, 32/64 bit, VST2/VST3 dplicate installations etc.
However, I don't worry about the number as Sonar does a really good job scaning quickly. I don't install freebies at random or for the fun of it, so my system is "clean". I don't even bother about deinstalling old 32 bit versions because Sonar does a great job hiding them (and there might be a chance you need them in other applications like video editing software etc.).
But I do use my custom plugin list to access the go-to plugs quickly and have the less frequently used ones only a sub-menu or two away. I reorganise that list a few times a year and have the same list on main and backup system and live system (although the live system contains much fewer plugs but by itself presents me with a shorter but still custom list)