H.W.
I love the Oregon coast. I've lived in Oregon since I was about 6 and still adore it. Kind of bummed that the husband wants to go to Seattle for this summer vacation, but anyway...
Cannon Beach is nice, but not great for beachcombing usually. (Which is our favorite beach activity besides sandcastles and dams!) Very busy tourist town, which is cute and nice but busy. Going down the coastline, Seaside is also very touristy; Lincoln City is popular and does end up having a lot of traffic, though.
If you are looking for tidepools, the beach around Seal Rock is great. Seal Rock is about 15 minutes or so south of Newport. Newport itself has a cute waterfront area on Yaquina Bay; also has Nye Beach for a little more upscale shopping/food. There are lots of hotels in the area, a great aquarium and Rogue Brewpub, which is very family friendly. (make dinner reservations, though, we learned!) Newport also has some good beaches in the northern part of town as well as two historic lighthouses. Seal Rock State Park: it's a bit of a walk out to the tidepools, but very nice when you get there.
http://www.oregonstateparks.org/index.cfm?do=parkPage.dsp...
You might look around and see where the best rates are for lodging. Seal Rock (the town) is just a bit north of Waldport and the more rugged beaches of Yachats are a bit more south of that. It's a nice stretch of coastline. When we go, we stay at in Seal Rock and drive up to Newport.
I hope someone else can give you more information on southern Oregon Beaches.