I couldn’t say much about rentals, but some good landmarks include:

Sea Lion Caves, in Yachats, near Florence. Largest natural sea cave in.. the US? The world? I don’t recall. The historical aspect of it is interesting though, the old stone steps, etc.

The Astoria Tower, in Astoria. It’s a nice city too, in terms of restraunts, beaches, things to do.

Portland is a wonderful city with a huge variety of things to do, although it does rather lack beaches.

Florence is a small coastal town that’s gotten pretty popular as a tourist attraction. Very lush and green, some good restraunts, lots of sand dunes and the activities that go along with that, buggy rides, sand boarding, etc.

As long as you spend some time on the beach you won’t be missing much.