Parallel Programming - What Systems Do You Prefer?

atti_2410 asks: "As multi-core CPUs are finding their way into more and more computer systems, from servers to corporate desktops to home systems, parallel programming becomes an issue for application programmers outside the High Performance Computing community. Many Parallel Programming Systems have been developed in the past, yet little is known about which are in practical use or even known to a wider audience, and which are just developed, released and forgotten. Or what problems the actual users of parallel programming systems bother the most. There is not even data on the platforms, that parallel programs are developed for. To shed some light on the subject, I have setup a short survey on the topic, and I would also very much like to hear your opinion here on Slashdot!" What Parallel Computing systems and software have you that really made an impression on you, both good and bad?