I've often used Inquisit to run psychological experiments online. The software enables delivery of stimuli (e.g., text, images, etc.) and collection of reaction times. Obviously general purpose ...
I've used E-prime to create computer based psychology experiments (you know, the kind where you for example show a number of pictures to the participant and record their responses to them, for example ...
I find the IPad to be a great piece of hardware that is easy to bring along and that has an intuitive touch interface. This would make it an ideal platform for many cognitive tests such as n-back. As ...