I recently learned about these cups, made of corn. They look just like plastic drink cups, but they are compostable (180 days in a municipal compost facility, or 1 year if home composted).
They are also made from a renewable resource, rather than petroleum, and they cost the same or less than plastic cups.
Warning: nothing decomposes in a landfill, so it's still better to use reusable cups and dishes!
But if you're planning to enjoy any upcoming beautiful days with an outdoor party, and you're planning to use plastic cups, utensils and/or paper plates (or if you know a community group that is), check out the renewable, compostable products at WorldCentric:
Plates made from sugar cane pulp (that would otherwise be burned, contributing to green house gas pollution).
Utensils made from potato starch
You get the idea...there's more at the store.