G.L. Pease Gaslight (very heavy latakia. Plug Cut)
Cornell and Diehl Super Balkan (A medium bodied English. Ribbon/broken Flake cut)
Mac Barren HH Pure Virginia (light, sweet, rich. 100% Virginia. Flake cut)
Cornell and Diehl Kajun Kake (dark, tangy, spicy. Virginia and perique. Cake cut)
I believe these 4 will give you a broad spectrum, representative of the major flavor profiles that pipe tobacco offers.
I would add 2 more for a more complete representation though.
Seattle pipe club Mississippi River (a nice balance of sweet, sour, and toasted)
Mac Barren HH old Dark fired (a nice BBQ smokiness)