The Idylls of the King is a series of twelve narrative poems in blank verse that recount the legend of King Arthur. Though the poems are set in the distant past, many of the ideals set forward are representative of the Victorian age in which Tennyson lived. Individual poems follow the stories of certain knights or other important figures, like Lancelot and Merlin, and the overall arc of the epic tells the story of Arthur's rise to power and his eventual death.
Boasting the largest collection of book summaries, BookRags is the best option for titles you can't find elsewhere. They offer all of the basics (quotes, chapter summary, characters, historical context, literary criticism) but also walk through a few major topics that recur throughout the book, which can be particularly useful for essay writing.
The original provider of professionally-written study guides, Cliffs Notes were available in print form before the Internet even existed. Their content is very comprehensive and includes an analysis of characters, detailed chapter by chapter summaries, critical essays, essay topics, and many other sections.