I agree with skunkride on the DJ part effect. Colour Barrier by Leroy Brown & Clint Eastwood springs to my mind. As for dub, I always love the mix on Youthman In The Ghetto by Prince Alla. Musical genius by Scientist.
I've always loved the Jacob Miller - Keep On Knocking 12" when it comes to this.
A great tune churning away and then a little hint of some mix, and the restart with the test tone, cutting through announcing the dub.. and it's a subtle sonic treat to start the dub mix with plenty of teasing drop outs and echo.