I love the VQ series engine (non GT-R) The VQ37HR. It revs high and fast, lots of power and great sound. the power is just there, its not smooth its wild and for that i love it.

I love the N54B30 (BMW I6 3.0 Twin Turbo) Its a great engine with great sound and SO MUCH POWER! Its very smooth (except at idle) and the power is so abundant you can't even feel it you just see your speedometer go up up and away. its very fast and very powerful.

And how can we forget the Boxer 6 engine. like the 911 Carrera S 997. What an amazing sound. Add a pair of turbo's and WOW.

I can't ignore good old American V8's (particularly Chevrolet)
And on that note i love the 4.2L Audi V8 in the S5. It sounds so nice, grumbles like crazy at idle and from nought to 3k rpm its loud but after that it gets smooth and quiet. have you ever heard an engine smoothen out and become quieter as it get up in the RPM? it makes it kind of hard to rev match but its really nice.

There are many other good engines out there too. Those are a few of my favorites.