I am basically with Nick.
I plant most of my stuff in particular brassicas approx 15" apart both ways.
This fits in with my bed system where my beds are roughly 5'-0" to 5'6" wide meaning I can get four plants across the bed. e.g.
8" X 15" X 15" X 15" X 8"
I find these distances work well for hoeing plus I can get my rake between the rows to clear the hoed weeds.
Another thing is; as the plants mature they tend to be 'goblet' shaped and subsequently support each without overcrowding each other, thus avoiding the need to stake taller varieties.