For the patio, I decided to go all out. I wanted a way to both stream the music and charge the phone at the same time. I didn't really want to buy a dock, though, since both of our phones are in cases, and while the cases typically don't fit well in docks, they do tend to accept docking cables.
So I bought the Apple Composite AV cable. The idea is that the audio will plug into another one of those Jameco audio amplifier kits, and the speaker wires will go through the wall to outdoor speakers. The iPhone end of the AV cable will sit on a little shelf just inside the patio door.
The cable is a little bit expensive, but it does include a USB power port. One of Apple's "sugar cube" chargers and a dock cable are by themselves almost as expensive as this cable.
One note, though is that whenever this cable is connected, the internal speaker of the phone is disabled. All the UI sound effects go out the cable instead. Also, whenever the cable is connected, YouTube and the iPod video playback don't actually play on the iPhone's screen. Instead, they play out the video cable and you get a still image on the iPhone screen. Also, the phone's UI does not display on the TV.
The "genius" at the Apple store actually got that wrong. He said that the video would play on both screens.
But I'm actually reasonably satisfied with the result. I don't plan on playing video while it's connected this way, though I suppose I could use a projector and one of those outdoor inflatable screens to do an outdoor movie night...