I would say all of the very well-known blends, even if it's a bit of a boring answer for the experienced pipe smoker. For example:
- Nightcap
- Full Virginia Flake
- Capstan Blue
- Deluxe Navy Rolls
- Stokkebye Luxury Navy Flake or Bulls Eye Flake
- Peterson (Dunhill) Flake
- GLP latakia blends (Westminster and Quiet Nights IMO)
- Boswell aromatics
- Various codger blends
And if you want to get into some worthwhile unicorn blends or discontinued blends:
- Frog Morton series
- McClelland virginias (I would not personally recommend shelling out the big bucks for McC virginias, but I understand why people like them, and they are pretty unique)
- Esoterica Penzance
Of course once you smoke all the well-known blends, then you branch out from there, which perhaps is what this thread is really about. I just wanted to make the point that it makes sense to become well-versed in the basics, which will give you a better framework for appreciating more unique or exemplary blends.