To tempt people into shedding some cash up front, Cryptic is prepared to dangle guaranteed beta invites to those who purchase a $60 or $200 pre-order Founder's Pack. In addition to the closed beta access, the $60 version contains a head-start to the open beta, a title, an armored horse mount, a mask, and a direwolf companion. The $200 pack has an even longer open beta head start, an exclusive Menzoberranzan Renegade playable race, a closed beta code for a friend, a spider mount, a panther companion, and priority access to the game.
Alternatively, Cryptic's offering a $20 basic pack that will not contain a closed beta key, but will give players a few in-game items and 12 additional inventory slots.
[Thanks to Paul for the tip!]