I haven't tried too many 20-year-old scotches, though I once had a glass of Highland Park 21 or 23 and it was mighty tasty. Highland Park 18 is pretty good. As per blends, I favor Johnnie Walker Gold Label (18) and Famous Grouse 18-year-old.
For a great deal, you can't beat HP 12-year-old, and the Talisker 10 is a classic.
Who is going to partake in a $20 CCME internet toast with me? I'm going out and picking up a nice 20 year single malt scotch for the occasion.