Well, certainly John Keats is defined as the epitome of a Romantic poet. One aspect that is hard to ignore in his poetry is the predominance of the imagination. An excellent poem to use to talk about this aspect of Romanticism is "On First Looking into Chapman's Homer," which talks about when Keats first read a translation of Homer's Illiad and how it came alive to him so vividly that he compares that moment to when new explorers look upon undiscovered plains:
Then felt I like some watcher of the skies
When a new planet swims into his ken;
Or like stout Cortez when with eagle eyes
He stared at the Pacific--and all his men
Looked at each otehr with a wild surmise--
Silent, upon a peak in Darien.
Note the way that the imagination is celebrated in this flight of fancy. This is a key aspect of Romanticism, as the imagination and feeling is always much more important than reason.
Secondly, you might want to focus on the topic of beauty as discussed in "Ode on a Grecian Urn." This excellent Romantic ode focuses on the pictures painted on a Grecian urn and how they cause the speaker to meditate on beauty and its eternal nature. Note how the poem closes:
When old age shall this generation waste,
Thou shalt remain, in midst of other woe
Than ours, a friend to man, to whom thou say'st,
"Beauty is truth, truth beauty,"--that is all
Ye know on earth, and all ye need to know.
There is a strange ambiguity in these lines, especially the quote of "Beauty is truth, truth beauty," which focuses our minds on the way inwhich the quest for beauty is positive in that the contemplation of ideal beauty gives us an experience of the timeless and eternal, but at the same time it is negative as such eternal beauty acts as a powerful reminder of our own ephemeral nature. Such discussions on beauty and its importance to our lives are another aspect of Romanticism.