What PC keyboards allow for 6-key braille data entry?

This gets tricky. Braille 6-key entry requires a feature called "n-key rollover". Often keyboard designers leave out n-key rollover to save a few pennies. So the short answer is some keyboards work, and some do not.

Sadly, vendors change products all the time, and a very subtle design change can mess up braille keyboard functionality even though the product's model number may not have changed. Before you pay good money on a keyboard, we always recommend that you take the particular one you're buying and perform the following test:

In a Windows computer click Start then Run. In the space provided to type a file name press the six keys SDFJKL SIMULTANEOUSLY at least seven times. Then press Backspace to clear the box and then press the six keys once more. All six letters must show but the order does not matter. If you do not have Windows you can run the same test at the DOS command prompt. If you cannot get all to show then you will not be able to braille multi-dot characters reliably with that keyboard in ANY six-key input braille program.