HP 12C
It started selling the financial calculator in 1981, the same year IBM Corp. introduced the personal computer. Today, with very few changes, the 12C is still HP's best-selling calculator. With its mortgage amortization and bond calculation functions, it is as essential to many real estate salespeople as a smile and firm handshake. When introduced, the calculator sold for about $150 -- more than $305 in current dollars. Today it retails for about $70. (via Fark)
