The Screaming Bird is horrible. HBE is out of business. I have a tonne of boost pedals, and even one anti-boost.
My favourites right now are (in no order): z.vex SHO, Bogner Harlow, AnalogMan Beano Boost.
If your are looking for the Richie Blackmore thing, a friend of mine LOVES his Dunlop Echoplex preamp.