It would be great to have:
I imagine a xmarginal and ymarginal (marginal for both) keyword arguments taking: :boxplot, :histogram, :density, :ticks or a combination of those symbols (tuple).
These are all good ideas as recipes... I don't think they should be "built in" for Plots.
marginal histograms
marginal density plots
marginal boxplots
I need to allow a little more control over subplot layouts, but this should be done with linked subplots:
using Plots
pyplot(size=(500,400), grid=false)
n = 10000
x, y = randn(n), randn(n)
subplot(
histogram(x),
plot(),
histogram2d(x, y, nbin=10),
histogram(y, orientation=:h),
link=true
)
marginal ticks
A nice implementation would require the ability to draw over the plot... this functionality will vary heavily by backend. I'm open to implementation ideas.
See #60
These are going in https://github.com/JuliaPlots/PlotRecipes.jl

That's awesome! :)
That is super cool! Yay for recipes
closing in favor of "Recipe ideas" issue
Most helpful comment
These are going in https://github.com/JuliaPlots/PlotRecipes.jl