2 row is the biggie. You'll go through 8-15 pounds or so in each batch, Pils, Maris Otter, and Belgian 2 row are the three that I like, but it depends on what styles of beer you're making.
Wheat is handy, especially in the summer time. Not only do you need it for your wheat beers, but it can be used as a specialty malt as well- a pound or so in a batch will aid head retention.
In Process: Mango Beer, Homebrewers Pale Ale
Bottled/Kegged:Spicy Light Rye, Rice-adjunct Pale Ale, Mild Bourbon Porter, Roasty Stout, Basic Light Mead, Bourbon County Stout Clone
Up Next: Berlinerweiss, Chocolate Raspberry Ale, and American IPA