We finally broke down and bought a rain barrel. OK, I broke down; Debbie had been advocating for it for a long time. I didn't want a big honking ugly contraption sitting in our yard, and what I'd seen seemed awfully expensive. But we ran across one at Home Depot for $99 - about half the price we'd seen at local nurseries - and it holds 57 gallons, has a spigot and an [almost] airtight lid, and comes with a downspout connection kit which will come in handy should we ever have a downspout. (I'm not going crazy with all this.)
And as far as having an ugly contraption in our yard...well, have you seen our lawn lately? Having an industrial vessel as a distraction from the dying grass is actually a benefit.
Now that we have it, I have to agree it's quite handy. As documented earlier, we're now hauling gray water each day to keep trees and major shrubs hydrated. On days where watering isn't required (but bathing/showering is) we can dump the multiple five-gallon buckets into the barrel for storage. Or, on those days where more than 40 gallons is needed (which is our normal daily haul), we can withdraw extra. The spigot can even be attached to a regular garden hose for hand-watering, although we haven't tried that yet.
But the best use for a rain barrel is to collect, you know, rain. And we finally got to do that early this morning. I had the proud foresight to leave the lid off and here's the welcome result: