Well, on the stregnth of all the recommendations here, I've just bought a bottle for New Years Eve.Looking forward to it.
I hope it'll live up to the hype!
I tried a lot of Proseccos of different price ranges (I was a bit of a lush), but the best I found in a supermarket was definitely this:
About the only good thing Sainsbury's does.
I used to see it on offer for a fiver at times! As good a quality as many of a fancier price tag. *Sigh* I do miss the holiday drinking, but my waistline and wallet are very grateful I've stopped.

Looking forward to it.