The area surrounding Haystack Rock is a naturalist's paradise. Kept clean by law, you can hike across the sandy beaches along the coastline from the town of Cannon Beach (it's actually less than a quarter-mile walk, so it's not really a hike at all, per se.).
At low tide, there are incredible, clear tidal pools filled with plant and animal life waiting to be discovered. You can also climb over some rather large rocks to get onto Haystack Rock itself, provided that it's not Puffin mating season -- during those times, since the Puffin is protected in Cannon Beach, you won't be able to go onto the rock itself. (The Puffin, by the way, is a bird that looks a lot like a penguin, but flies. You'll see a lot of them in Cannon Beach.)
One note of caution: Know the tide schedule. Almost anywhere in town has a Cannon Beach Gazette, and you'll want to look up those tables before you head out onto the rock. If the tide comes in -- and it does so very rapidly -- you could be stranded on the rock with very deep, very fast, pounding waves all around you. The Coast Guard has to be called quite often to rescue poor stranded souls.
It is a very popular location among pacific northwesterners, I'm warning you now. This means that finding alone-time during the low-tide hours of the summer is nearly impossible. I know from experience that there is no way to get a full sketch of anything in a tidepool done without several people of varying ages interrupting to ask what you're doing, or to comment on your work. People are friendly to a fault, which is both a good and bad thing, depending on your activity.
The majority of the beach is also protected from the removal of objects. Don't head here if you're looking to collect sand dollars or shells -- you won't find any, and if you -do-, you're not allowed by law to take them with you when you leave. They are strict about this, and although most of the beach patrols won't give you a $500 ticket, they are allowed to -- and might if you cop an attitude.
The sea rolls in here with an overwhelming roar. Despite the crowds, it is one of the most beautiful places in Oregon to watch the sunset -- and there's a local legend that says that as the sun dips finally over the Pacific, there is a flash of green. Photographers have tried to catch it -- whether they have or not, I'm unaware. It's still wonderful to watch.
Two other monoliths share the surrounding area, neither is accessible, even at low tide.
This is possibly my favorite place along the Oregonian coast. At the whopping cost of free, you can't find any better than this.