My boss and I were talking about astronomy-related things (him being a big amateur astronomer), when he brought this up: the Interplanetary Transport Network. Relying on varying Lagrange points, it is possible to work your way through parts of the solar system for an absolutely small amount of fuel.
This came up after talking about the old ideas for thermonuclear bomb-propelled spacecraft, in comparison to some recent advances in ion thrust technology. Before that was talking about Hubble’s astigmo-optics (how its mirrors were misground, and had to be repaired in space).
Of course, the ITN network is circuitous, which isn’t too surprising, I figure. However, it would likely be a great way to run automated resupply missions that are planned well ahead of time.