DX11 opens the doors for a much easier ways of working with particles for example due to its Geometry instancing feature.
Check these amazing contributions:
Particles (2d Field)
Particles (2d ForceField)
Particles (3d Field)
Besides the nodes from the Addonpack contributed by vux (see left column) there are two powerful particle system contributions:
There is also this very comprehensive guide written by dottore about DX9 GPU particles.
This forum thread is an interesting read about CPU-based particles. And vvvv's c#-utility library comes with a simple Particle Class which should be a good start for simple CPU particles.
And don't forget the related contributions by other users: