Honddaribia, right at the doorstep of some good riding. Nice town too.
Mundaka, on the Gernika estuary. Again, good biking and nice town. More for surfers though. (the longest left-break in world, whatever that means)
Sopelana, near the cliffs, there's a good singletrack ride next to i. (it's my local ride). There's a metro for Bilbao too.
Plentzia, bit further along from Sopelana, nicer town and the beach is excellent.
Inland, Potes, there's a few and you've got the Picos de Europa to ride in.
Gijon, basic, does the job, it's a nice town too. Right on the cliff tops.
That's just the ones i've been to.
As for the wild caming, reckon the poster was lucky, as it's definitely not accepted. (police rapping on tent teling you to move on type of thing)
oh, and you can camp in my garden if you want.