Fern Canyon and the Tall Trees trail are fun hikes, but you have to get advance permits. Worth it to do so. Redwood is a patch work of state and federal parks. Some other hikes that are worth it:

Damnation Creek trail
Grove of Titans (very easy)
Ladybird Johnson (very easy, but lots of Redwoods)
Enderts Beach (very easy)

Crater Lake is inland but if you are trying to check off national parks, totally worth the effort.

Hoh is worth it, but Quinault is also good if you are pressed for time.