[sworthy]

I just ordered a Sonos system for the backyard, but have absolutely zero experience with outdoor speakers. Anyone have any recommendations? I'm in San Francisco, so I assume the speakers will hold up fine outdoors, even with heavy at times rain? The yard is fairly small, and I don't want to have everyone on the whole street hear the music, so those 360 degree speakers are out.

[d.fine]

B&W has outdoor speakers, not too big, good sound, and wheatherproof. They're not too expensive either, and easy to hang up.
In the product range, check under Leisure Monitors, then chose the WM series.

[Nivag]

i've just found these while looking for some outdoor speakers

The Staddle Stone speaker also features 360-degree sound dispersion and will compliment your garden and patio.

Hand cast in beautiful reconstructed Bath stone you will be surrounded by music in your garden and friends will be amazed.

more info here - http://www.gardensound.co.uk

otherwise these are more normal looking

Features
Fully Waterproof
2 year warranty
8 ohm low impedance (li) when driven by a conventional HiFi
Massive maximum potential output of 100W (50 Watts RMS)
Supplied with stainless steel corrosion resistant brackets
High quality UV stabilised corrosion proof ABS plastic basket
PP mica injection cone with TPU surround
Corrosion proof silicone coated terminal wire
UV stabilised and corrosion proof and acid/alkali resistant mesh.
Available in 2 colours: Black or White
Dimensions: 233x157x178(mm)
http://www.aqsound.com/store/en/view_product/101/