Both the millet and ornamental corn are annuals and very easy to grow from seed, although starts are available at better area nurseries. New Zealand flax is not a grass at all but a flowering, evergreen perennial in the agave family. It comes in a huge range of sizes and colorings but is unlikely to be hardy in climates other than the south or colder than the PNW.

Other than the tender forms and 'Karley Rose', I've never been a big fan of Pennisetums. Very late to emerge, messy looking and late to bloom as well. For smaller grasses I prefer pretty much any carex, but Anemanthele lessoniana wins my vote for all-round best looking grass in any season.