There's a reason I'm starting with water. I don't know about the rest of y'all, but where we are has been pretty dry for a couple of years now. Stupid drought. What rain we do get I try to hoard, instead of letting it run out the downspout to water the lawn, which is inedible and therefore useless to me. I try not to water the garden with city water, because that costs money. I put in the vegetable garden to SAVE money, so free water suits me just fine.
Below are my two big rainwater reservoirs, made up of two IBC's (Intermediate bulk containers) I got for cheap from a guy selling them on CL. We rerouted the downspout a little, stuck on one of those accordion plastic rainspout thingys from the hardware store (see below), and covered it with temporary reed fencing from the garden section because IBC's are ugly and this is visible from the street. The two IBC's are connected to each other with two shower drains (with the grates removed) and a short length of PVC pipe, sealed together with a bit of silicone. When one fills, the overflow runs into the second IBC. The holes in the side of the IBC's for the shower drains were cut with a jigsaw. I'll try to get a better picture of the linking if anyone's interested.
On the other side of the house I got a "rain barrel" kit, because an IBC wouldn't fit in my flower bed. It does the trick, but cost more than an IBC and doesn't hold near as much water.