And really, based on my constant scouring of this place, a good place to start would be with...
ASUS and Gigabyte MOBOs (so whatever BIOS/Utility/connectivity/chipset stuff that goes with that)
Focusrite, RME, PreSonus and Roland QuadCap interfaces (and their drivers)
Win7, 8 and soon 10 optimization tweaks (obviously)
Third party plugs (Waves, Izotope, Steinberg, IK, XLN, FXpansion)
AVs (Microsoft Security Essentials, AVAST, Kapersky... and really if you are using anything else you probably should switch IMO) and extras like CCleaner, Malwarebytes, Spybot S&D... all of which have settings that cause automatic thingies to happen that may interrupt data flow.
Common apps like Office, web browsers, flash players, etc that may call home or do weird stuff on startup.
Just some thoughts based on observations of our user base.