I mentioned horizon graphs [previously](http://michaelgalloy.com/2009/01/26/horizon-graphs-in-idl.html), but didn't give the code for producing them. Here's the [`VIS_HORIZON`](http://michaelgalloy.com/wp-content/uploads/2009/05/vis_horizon.pro) routine ([docs](http://michaelgalloy.com/wp-content/uploads/2009/05/vis_horizon.html)), but you will need [`VIS_LOADCT`](http://michaelgalloy.com/wp-content/uploads/2009/05/vis_loadct.pro) and the [Brewer color table file](http://michaelgalloy.com/wp-content/uploads/2009/05/brewer.tbl) to run the example program i.e. `.run vis_horizon`. UPDATE: you also need [`VIS_SRC_ROOT`](http://michaelgalloy.com/wp-content/uploads/2009/05/vis_src_root.pro).
I've found horizon graphs are a good choice as an alternative to using `OPLOT` many times. The different line plot series quickly become crowded where the horizon graphs don't interact as much and still maintain a fairly good ability to be compared to each other.