For F1 sounds i always thought the Farrari V12's sounded best.
YouTube - 1994 Scuderia Ferrari F1 V12

As for street cars I have always loved the sounds GM's LSX V8 motors can make.

YouTube - LG Motorsports - G6X1 Cam for LS3 - Dyno Video - Sound Clips

YouTube - 2006 GTO FLOWMASTER 10 SERIES MUFFLERS
I still want to try delta 10 on the x-fire one of these days