Redwood NP is great - but be aware that there is a federal section (near Orick) and 3 or 4 Redwood State Parks that are co-managed with the federal National Park. Those SPs (Prairie Creek, Del Norte, Jedediah Smith) are arguably better than the National Park (unless you wish to backpack, in which case Redwood Creek is about your only option).
In addition, the Humboldt Redwood State Park has the most dense concentration of big redwoods anywhere, and in my opinion is every bit as good, if not better, than the 4 Natl Park segments slightly north of there. The Bull Creek Flats / Big Tree Loop (~10mile) is the best redwoods hike, IMO. At the very least, drive through/along the Avenue of the Giants.
2 days? Wow. Hard to recommend. I'd say 1 day each in Jed Smith & Prairie Creek. (Substitute Humboldt for either, and you won't go wrong.)
Damnation Creek Trail, mentioned above, (in Del Norte) is indeed awesome, but Boy Scout Tree Trail (in Jed Smith) is too, and the drive along the road through Jed Smith is amazing. But the most trail mileage is in Prairie Creek SP, and many people like the James Irvine / Miners Creek Loop the best.
One can also backpack the Coastal Trail, thru Del Norte, although there are some serious brush problems between Wilson Bay and that first backcountry campsite, and as beautiful as it was, the nettle nuisance is not worth that section. (Further along, though, the Damnation Creek Trail intersects the Coastal Trail, which continues north to nice backcountry sites at Nickel Creek.)
Your best resource for Redwoods Hikes is...
http://www.redwoodhikes.com/ Absolutely awesome website (and his maps are wonderful too - I own them all.) His ratings for best hikes would be pretty close to my own.
Bring ponchos, and go hike in the rain. The rainier the weather, the fewer people you'll see.
