Engine Trails and Dust
Wasn't such a good idea to mess with this guy...he has a lot of guns. I've upgraded engine trails to a first-class subsystem, they no longer use the particle system. They look much better as continuous ribbons rather than bunches of particles.
Last night I started playing with fake volumetric effects for nebulas/dust clouds/etc. The effect is really cool, but isn't that apparent in screenshots. When flying around, the effect is pretty compelling. This was one of my favorite graphical aspects of Freelancer - the look and feel of dust clouds. They felt so distinct and really broke up the monotonous feeling of space.