1) You need the Hallertauer for your Hefes and any German lagers.
2) You need either the Cascade or Centennial for APAs & IPAs.
3) You need either Willamette or Goldings for anything British in style.
The fourth one can be the second one from one of the categories above or Cluster. Cluster are one of the original US hop strains and are good for bittering & would work great for Cream Ales. In fact, I'd bet that they were the hop for many old school cream ales. I know that $6.95 price on HopsDirect is hard to turn down.
Currently On Draft: Bamberger Rauch Dunkel, Belgian Blond, Pilsener Urquell clone, Smoked Porter
Bottled: Concord Pyment, Mi'Apa Sparkling Mead, Chimay Blue, Old Simcoe American Barleywine, Old Cantankerous
Fermenting and Conditioning: Pseudo-Decoction Munich Dunkel, Left Hook Bitter
Recently Kicked Kegs: Fresh Hop Pale Ale, Citra Rye IPA
On Deck: Old Rasputin, Northstar IPA, Ur-bock Dunkel