Say what you will about Berkeley (insert snarky comment here about the hazards of the Berkeley Bowl parking lot), but they do know how to pick their grasses. Carex divulsa or Berkeley Sedge (formerly Carex tumicola) is one of those easy grasses that just flops over and looks like it recently started using volumizing shampoo. Plant a few for that carefree garden that doesn't care if it's shirt is tucked in. I should note, however that this grass is native to Europe and NOT California for you purists out there.
Soil: Not too picky, but ideally light clay I think.
Sun: Part sun, but can take full sun with more water
Plant: Anytime. These guys are tough.
Buy it: Annie's of course carries it and has a great photo to boot. Your local nursery should carry it and if they don't, ask them to.
Good for: Filling in spaces in new plantings, adding textural interest among the flowers, creating a dog friendly, lumpy lawn.