Snapping a point to another obejcts point?

Title says it all really, how can I snap a point of one object to a point of another object?

Yes I could extrude a face of the first object, separate it, then use that to start forming the second object, but… I’d sooner create the second object first, then tweak it to match it up.

And I can’t have everything in one object as the required animation is a kind of exploded diagram.

Thanks.

Snapping options on the 3d view header https://www.blender.org/manual/editors/3dview/transform/transform_control/precision/snap.html