New Zealand has recently changed their immigration laws, but in return for your investment (which starts at NZ$1.5 million), you get permanent residence only.

New Zealand has recently changed their immigration laws, but in return for your investment (which starts at NZ$1.5 million), you get permanent residence only. The investment has to be in a viable business (property does not qualify, obviously, nor does deposit in a bank), and cannot be for personal use. Citizenship takes 5 years of residence, like most places. I don't think any country will sell you citizenship (at least, not any country you'd want to go to :)