The HP-12C is HP's longest and best-selling product, in continual production since its introduction in 1981. Due to its simple operation for key financial calculations, the calculator long ago became the de facto standard among financial professionals – for example, most investment banks issue HP-12Cs to the members of each incoming class of its investment banking analysts and associates.

In 2008, HP modified the design so that new production runs contain an ARM processor which runs an emulated version of previous chips. This has brought advanced possibilities such as flashing new firmware, not previously possible. HP also released a software development kit (SDK), making it possible to make new and custom operating systems. The calculator runs 20 times faster on most benchmark operations. This version is colloquially known as the HP-12C+ although HP does not market it as a different product. This is the version sold by TheCalculatorStore.com.

Finally, here you have one of the two new "old" calculators: the 30th Anniversary HP12c

We have now units in stock.

Some quotes from Wikipedia:

The HP-12C is HP's longest and best-selling product, in continual production since its introduction in 1981. Due to its simple operation for key financial calculations, the calculator long ago became the de facto standard among financial professionals – for example, most investment banks issue HP-12Cs to the members of each incoming class of its investment banking analysts and associates. 

In 2008, HP modified the design so that new production runs contain an ARM processor which runs an emulated version of previous chips. This has brought advanced possibilities such as flashing new firmware, not previously possible. The calculator runs 20 times faster on most benchmark operations. This version is based on the same hardware, better packaged and with a more evolved firmware (dating from July 2009 as opposed to November 2008. No idea of what the changes were). It is important to underline that this calculator is not substantially different from the HP12c+ except on minor details and much better packaging.

This is the latest iteration of the HP12c - and it may well be the last. This package is a Collector's Edition, with a gift box, slightly thicker plastic pouch compared with the plain 12c, basic manual and a CD with the whole manual set. Excellent as a gift for a friend.

For business professionals and students, the versatile HP 30b Business Professional has an intuitive layout, high-speed processor and 2-line display for fast answers. Add custom calculations for school or work with convenient programming capability.