Poetry Foundation
Poetry Foundation: Baseball Poems
A collection of descriptive and metaphorical poems about baseball, including poems by Mae Swenson, John Updike, and William Carlos Williams, and, of course, "Casey at the Bat" by Ernest Lawrence Thayer.
Other
Poetry4 Kids
Author Kenn Nesbitt's poems are entertaining. Funny tongue twisters and popular poems such as "I'm Practically Perfect" are read by the author. There are also links to books and games.